Development of a regional GPS-based ionospheric TEC model for South Africa
- Opperman, Ben D L, Cilliers, Pierre J, McKinnell, Lee-Anne, Haggard, Raymond
- Authors: Opperman, Ben D L , Cilliers, Pierre J , McKinnell, Lee-Anne , Haggard, Raymond
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6799 , http://hdl.handle.net/10962/d1003925
- Description: Advances in South African space physics research and related disciplines require better spatial and time resolution ionospheric information than was previously possible with the existing ionosonde network. A GPS-based, variable degree adjusted spherical harmonic (ASHA) model was developed for near real-time regional ionospheric total electron content (TEC) mapping over South Africa. Slant TEC values along oblique GPS signal paths are quantified from a network of GPS receivers and converted to vertical TEC by means of the single layer mapping function. The ASHA model coefficients and GPS differential biases are estimated from vertical TEC at the ionospheric pierce points and used to interpolate TEC at any location within the region of interest. Diurnal TEC variations with one minute time resolution and time-varying 2D regional TEC maps are constructed. In order to validate the ASHA method, simulations with an IRI ionosphere were performed, while the ASHA results from actual data were compared with two independent GPS-based methodologies and measured ionosonde data.
- Full Text:
- Date Issued: 2007
- Authors: Opperman, Ben D L , Cilliers, Pierre J , McKinnell, Lee-Anne , Haggard, Raymond
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6799 , http://hdl.handle.net/10962/d1003925
- Description: Advances in South African space physics research and related disciplines require better spatial and time resolution ionospheric information than was previously possible with the existing ionosonde network. A GPS-based, variable degree adjusted spherical harmonic (ASHA) model was developed for near real-time regional ionospheric total electron content (TEC) mapping over South Africa. Slant TEC values along oblique GPS signal paths are quantified from a network of GPS receivers and converted to vertical TEC by means of the single layer mapping function. The ASHA model coefficients and GPS differential biases are estimated from vertical TEC at the ionospheric pierce points and used to interpolate TEC at any location within the region of interest. Diurnal TEC variations with one minute time resolution and time-varying 2D regional TEC maps are constructed. In order to validate the ASHA method, simulations with an IRI ionosphere were performed, while the ASHA results from actual data were compared with two independent GPS-based methodologies and measured ionosonde data.
- Full Text:
- Date Issued: 2007
Figuring maternity: Christine Dixie's Parturient Prospects
- Authors: Schmahmann, Brenda
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/147748 , vital:38667 , https://doi.org/10.1080/00043389.2007.11877068
- Description: The Interior, Birthing Tray and Parturition are three sub-sections of a project entitled Parturient Prospects that artist Christine Dixie began in 2005, when she was pregnant with her second child, and completed by the end of 2006. In Parturient Prospects, the author reveals, Dixie situates her experiences against Western discourses, especially images from early modern Europe. Focusing on the ways in which visual representations construct woman as ‘other’, Dixie invokes reference to not only representations of birth and maternity but also religious, medical and geographical images.
- Full Text:
- Date Issued: 2017
- Authors: Schmahmann, Brenda
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/147748 , vital:38667 , https://doi.org/10.1080/00043389.2007.11877068
- Description: The Interior, Birthing Tray and Parturition are three sub-sections of a project entitled Parturient Prospects that artist Christine Dixie began in 2005, when she was pregnant with her second child, and completed by the end of 2006. In Parturient Prospects, the author reveals, Dixie situates her experiences against Western discourses, especially images from early modern Europe. Focusing on the ways in which visual representations construct woman as ‘other’, Dixie invokes reference to not only representations of birth and maternity but also religious, medical and geographical images.
- Full Text:
- Date Issued: 2017
Global diversity of mayflies (Ephemeroptera, Insecta) in freshwater
- Barber-James, Helen M, Gattolliat, Jean-Luc, Sartori, Michel, Hubbard, Michael D
- Authors: Barber-James, Helen M , Gattolliat, Jean-Luc , Sartori, Michel , Hubbard, Michael D
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:7002 , http://hdl.handle.net/10962/d1008361
- Description: The extant global Ephemeroptera fauna is represented by over 3,000 described species in 42 families and more than 400 genera. The highest generic diversity occurs in the Neotropics, with a correspondingly high species diversity, while the Palaearctic has the lowest generic diversity, but a high species diversity. Such distribution patterns may relate to how long evolutionary processes have been carrying on in isolation in a bioregion. Over an extended period, there may be extinction of species, but evolution of more genera. Dramatic extinction events such as the K-T mass extinction have affected current mayfly diversity and distribution. Climatic history plays an important role in the rate of speciation in an area, with regions which have been climatically stable over long periods having fewer species per genus, when compared to regions subjected to climatic stresses, such as glaciation. A total of 13 families are endemic to specific bioregions, with eight among them being monospecific. Most of these have restricted distributions which may be the result of them being the relict of a previously more diverse, but presently almost completely extinct family, or may be the consequence of vicariance events, resulting from evolution due to long-term isolation.
- Full Text:
- Date Issued: 2007
- Authors: Barber-James, Helen M , Gattolliat, Jean-Luc , Sartori, Michel , Hubbard, Michael D
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:7002 , http://hdl.handle.net/10962/d1008361
- Description: The extant global Ephemeroptera fauna is represented by over 3,000 described species in 42 families and more than 400 genera. The highest generic diversity occurs in the Neotropics, with a correspondingly high species diversity, while the Palaearctic has the lowest generic diversity, but a high species diversity. Such distribution patterns may relate to how long evolutionary processes have been carrying on in isolation in a bioregion. Over an extended period, there may be extinction of species, but evolution of more genera. Dramatic extinction events such as the K-T mass extinction have affected current mayfly diversity and distribution. Climatic history plays an important role in the rate of speciation in an area, with regions which have been climatically stable over long periods having fewer species per genus, when compared to regions subjected to climatic stresses, such as glaciation. A total of 13 families are endemic to specific bioregions, with eight among them being monospecific. Most of these have restricted distributions which may be the result of them being the relict of a previously more diverse, but presently almost completely extinct family, or may be the consequence of vicariance events, resulting from evolution due to long-term isolation.
- Full Text:
- Date Issued: 2007
Olive Schreiner in Rhodesia: an episode in a biography
- Walters, Paul S, Fogg, W Jeremy M
- Authors: Walters, Paul S , Fogg, W Jeremy M
- Date: 2007
- Language: English
- Type: text , Article
- Identifier: vital:6123 , http://hdl.handle.net/10962/d1004707
- Description: Readers of biographies of Olive Schreiner - except for the pioneering work of Vera Buchanan-Gould (see 1948, 198-99) - could be forgiven for doubting whether Olive Schreiner ever was in Rhodesia. Although her husband's edition of her Letters includes three which cover this journey (Cronwright-Schreiner 1924a), he makes no mention of it in his Life (1924), and it is not touched on either in First and Scott (1980) or in Stanley's impressive biographical chapter (2002). Arguably, it does nothing to alter the by now well-established outlines of Olive Schreiner's life; yet, as we shall see, the visit itself might have meant the premature end of that life. Moreover, it documents Schreiner's visit to two sites of immense importance to her : the 'Hanging Tree' in Bulawayo which features in the (deliberately shocking) photographic frontispiece to the first edition of Trooper Peter Halket of Mashonaland (1897), and, secondly, Cecil Rhodes's grave in the Matopos. In just over a decade (13 Aug. 1921), she too would lie in her chosen mountaintop tomb.
- Full Text:
- Date Issued: 2007
- Authors: Walters, Paul S , Fogg, W Jeremy M
- Date: 2007
- Language: English
- Type: text , Article
- Identifier: vital:6123 , http://hdl.handle.net/10962/d1004707
- Description: Readers of biographies of Olive Schreiner - except for the pioneering work of Vera Buchanan-Gould (see 1948, 198-99) - could be forgiven for doubting whether Olive Schreiner ever was in Rhodesia. Although her husband's edition of her Letters includes three which cover this journey (Cronwright-Schreiner 1924a), he makes no mention of it in his Life (1924), and it is not touched on either in First and Scott (1980) or in Stanley's impressive biographical chapter (2002). Arguably, it does nothing to alter the by now well-established outlines of Olive Schreiner's life; yet, as we shall see, the visit itself might have meant the premature end of that life. Moreover, it documents Schreiner's visit to two sites of immense importance to her : the 'Hanging Tree' in Bulawayo which features in the (deliberately shocking) photographic frontispiece to the first edition of Trooper Peter Halket of Mashonaland (1897), and, secondly, Cecil Rhodes's grave in the Matopos. In just over a decade (13 Aug. 1921), she too would lie in her chosen mountaintop tomb.
- Full Text:
- Date Issued: 2007
Pretopological and topological lattice-valued convergence spaces
- Authors: Jäger, Gunter
- Date: 2007
- Language: English
- Type: text , Article
- Identifier: vital:6827 , http://hdl.handle.net/10962/d1012337
- Description: We show that the classical axiom which characterizes pretopological convergence spaces splits into two axioms in the general Heyting algebra-valued case. Furthermore we present a generalization of Kowalski’s diagonal condition to the lattice-valued case.
- Full Text:
- Date Issued: 2007
- Authors: Jäger, Gunter
- Date: 2007
- Language: English
- Type: text , Article
- Identifier: vital:6827 , http://hdl.handle.net/10962/d1012337
- Description: We show that the classical axiom which characterizes pretopological convergence spaces splits into two axioms in the general Heyting algebra-valued case. Furthermore we present a generalization of Kowalski’s diagonal condition to the lattice-valued case.
- Full Text:
- Date Issued: 2007
Resistance or tolerance: an examination of aphid (Sitobion yakini) phloem feeding on Betta and Betta-Dn wheat (Triticum aestivum)
- De Wet, L R, Botha, Christiaan E J
- Authors: De Wet, L R , Botha, Christiaan E J
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6517 , http://hdl.handle.net/10962/d1005945
- Description: Engineering pest resistance into crops is important. However, the mechanisms of resistance are not clearly understood. In this study, we examined the effects of aphid feeding on Russian wheat aphid-resistant and -susceptible cultivars of wheat (Triticum aestivum L.); Betta-Dn and Betta, respectively, by the grass aphid, Sitobion yakini (Eastop). These cultivars were grown with or without aphid colonies. In each case, we examined the plants specifically for the formation of wound callose associated with the phloem, using aniline blue and fluorescence microscopy. We observed that aphid feeding stimulated the formation of wound callose in the susceptible cultivar, but that callose was comparatively reduced in the resistant cultivar of wheat. In a separate series of experiments, the xenobiotic, 5, 6-carboxyfluorescein diacetate was applied to attached sink leaves, distal to feeding aphids. When leaf segments were examined four hours after application, little evidence of phloem transport of the fluorescent cleavage product, 5, 6-carboxyfluorescein (5, 6-CF), was evident below known aphid-probed sieve tubes. Low levels or absence of 5, 6-CF indicates that either the aphids have successfully redirected sap to themselves, or that the phloem is no longer functional. In contrast, 5, 6-CF transport was evident below sites of aphid probing in Betta-Dn, suggesting that the phloem was still capable of long-distance transport. In addition, callose deposition was reduced in Betta-Dn leaf phloem and it is surmised that transport was not as affected by aphid feeding in the resistant cultivar. This indicates that the ‘resistant’ wheat cultivar may in fact be tolerant to aphid feeding by successfully overcoming the nutrient drain that feeding aphids imposed on the phloem transport system.
- Full Text:
- Date Issued: 2007
- Authors: De Wet, L R , Botha, Christiaan E J
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6517 , http://hdl.handle.net/10962/d1005945
- Description: Engineering pest resistance into crops is important. However, the mechanisms of resistance are not clearly understood. In this study, we examined the effects of aphid feeding on Russian wheat aphid-resistant and -susceptible cultivars of wheat (Triticum aestivum L.); Betta-Dn and Betta, respectively, by the grass aphid, Sitobion yakini (Eastop). These cultivars were grown with or without aphid colonies. In each case, we examined the plants specifically for the formation of wound callose associated with the phloem, using aniline blue and fluorescence microscopy. We observed that aphid feeding stimulated the formation of wound callose in the susceptible cultivar, but that callose was comparatively reduced in the resistant cultivar of wheat. In a separate series of experiments, the xenobiotic, 5, 6-carboxyfluorescein diacetate was applied to attached sink leaves, distal to feeding aphids. When leaf segments were examined four hours after application, little evidence of phloem transport of the fluorescent cleavage product, 5, 6-carboxyfluorescein (5, 6-CF), was evident below known aphid-probed sieve tubes. Low levels or absence of 5, 6-CF indicates that either the aphids have successfully redirected sap to themselves, or that the phloem is no longer functional. In contrast, 5, 6-CF transport was evident below sites of aphid probing in Betta-Dn, suggesting that the phloem was still capable of long-distance transport. In addition, callose deposition was reduced in Betta-Dn leaf phloem and it is surmised that transport was not as affected by aphid feeding in the resistant cultivar. This indicates that the ‘resistant’ wheat cultivar may in fact be tolerant to aphid feeding by successfully overcoming the nutrient drain that feeding aphids imposed on the phloem transport system.
- Full Text:
- Date Issued: 2007
The structural and functional diversity of Hsp70 proteins from Plasmodium falciparum
- Shonhai, Addmore, Boshoff, Aileen, Blatch, Gregory L
- Authors: Shonhai, Addmore , Boshoff, Aileen , Blatch, Gregory L
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6486 , http://hdl.handle.net/10962/d1006269 , http://dx.doi.org/10.1110/ps.072918107
- Description: It is becoming increasingly apparent that heat shock proteins play an important role in the survival of Plasmodium falciparum against temperature changes associated with its passage from the cold-blooded mosquito vector to the warm-blooded human host. Interest in understanding the possible role of P. falciparum Hsp70s in the life cycle of the parasite has led to the identification of six HSP70 genes. Although most research attention has focused primarily on one of the cytosolic Hsp70s (PfHsp70-1) and its endoplasmic reticulum homolog (PfHsp70-2), further functional insights could be inferred from the structural motifs exhibited by the rest of the Hsp70 family members of P. falciparum. There is increasing evidence that suggests that PfHsp70-1 could play an important role in the life cycle of P. falciparum both as a chaperone and immunogen. In addition, P. falciparum Hsp70s and Hsp40 partners are implicated in the intracellular and extracellular trafficking of proteins. This review summarizes data emerging from studies on the chaperone role of P. falciparum Hsp70s, taking advantage of inferences gleaned from their structures and information on their cellular localization. The possible associations between P. falciparum Hsp70s with their cochaperone partners as well as other chaperones and proteins are discussed.
- Full Text:
- Date Issued: 2007
- Authors: Shonhai, Addmore , Boshoff, Aileen , Blatch, Gregory L
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6486 , http://hdl.handle.net/10962/d1006269 , http://dx.doi.org/10.1110/ps.072918107
- Description: It is becoming increasingly apparent that heat shock proteins play an important role in the survival of Plasmodium falciparum against temperature changes associated with its passage from the cold-blooded mosquito vector to the warm-blooded human host. Interest in understanding the possible role of P. falciparum Hsp70s in the life cycle of the parasite has led to the identification of six HSP70 genes. Although most research attention has focused primarily on one of the cytosolic Hsp70s (PfHsp70-1) and its endoplasmic reticulum homolog (PfHsp70-2), further functional insights could be inferred from the structural motifs exhibited by the rest of the Hsp70 family members of P. falciparum. There is increasing evidence that suggests that PfHsp70-1 could play an important role in the life cycle of P. falciparum both as a chaperone and immunogen. In addition, P. falciparum Hsp70s and Hsp40 partners are implicated in the intracellular and extracellular trafficking of proteins. This review summarizes data emerging from studies on the chaperone role of P. falciparum Hsp70s, taking advantage of inferences gleaned from their structures and information on their cellular localization. The possible associations between P. falciparum Hsp70s with their cochaperone partners as well as other chaperones and proteins are discussed.
- Full Text:
- Date Issued: 2007
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