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Search Results: 1 - 10 of 382096 matches for " R de Klerk "
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Macroinvertebrate Assemblage Changes as an Indicator of Water Quality of Perennial Endorheic Reed Pans on the Mpumalanga Highveld, South Africa  [PDF]
Arno R. de Klerk, Victor Wepener
Journal of Environmental Protection (JEP) , 2013, DOI: 10.4236/jep.2013.47A002
Abstract:

Reed pans are a very uncommon type of endorheic wetland, and as such the amount of information available is very limited. Thus, they are being impacted on by various agricultural, livestock and other anthropogenic activities. The objectives of this study were to determine the spatial and temporal variations of macroinvertebrate community structures in reed pans and the environmental factors (i.e., water quality) responsible for the maintenance of these structures. Reed pans were studied over four different seasons, during which time subsurface water, sediment and macroinvertebrate samples were collected and analyzed. The reed pans studied showed that the macroinvertebrates were able to reflect various changes in reed pans with regard to seasonal variability and anthropogenic impacts on water quality. These anthropogenic impacts caused the disappearance of sensitive macroinvertebrate taxa and the increase of tolerant macroinvertebrate taxa.

The human genome project in clinical perspective: The emperor’s new clothes?
R de Klerk
Continuing Medical Education , 2005,
Abstract:
The development of a social-cognitive model for a better understanding of the female adolescent suffering from anorexia nervosa
E van der Spuy, HM de Klerk, R Kruger
Journal of Family Ecology and Consumer Sciences /Tydskrif vir Gesinsekologie en Verbruikerswetenskappe , 2003,
Abstract:
Plant communities of the Ebenhaezer section of the Mountain Zebra National Park
J. de Klerk,L.R. Brown,H. Bezuidenhout
Koedoe : African Protected Area Conservation and Science , 2003, DOI: 10.4102/koedoe.v46i2.47
Abstract: The long-term conservation of viable ecosystems requires a broader understanding of the ecological processes involved. Because ecosystems react differently to different management practices, it is important to have a description and classification of the vegetation of an area available. As part of a vegetation survey programme for the newly acquired farms to be incorporated into the Mountain Zebra National Park, the vegetation of the Ebenhaezer section was investigated. Ahierarchical classification, vegetation map, description and ecological interpretation of the plant communities of the study area are presented. ATWINSPAN classification, refined by Braun-Blanquet procedures revealed eight distinct plant communities. Habitat factors associated with differences in vegetation include topography, soil form and grazing. Descriptions of the plant communities include diagnostic species as well as prominent and less conspicuous species of the tree, shrub and herbaceous layers.
De Britsch-Indi rs in Suriname
C. de Klerk C.ss.R.
Nieuwe West-Indische Gids , 1941,
Abstract:
Small-Bodied Humans from Palau, Micronesia
Lee R. Berger, Steven E. Churchill, Bonita De Klerk, Rhonda L. Quinn
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0001780
Abstract: Newly discovered fossil assemblages of small bodied Homo sapiens from Palau, Micronesia possess characters thought to be taxonomically primitive for the genus Homo. Background Recent surface collection and test excavation in limestone caves in the rock islands of Palau, Micronesia, has produced a sizeable sample of human skeletal remains dating roughly between 940-2890 cal ybp. Principle Findings Preliminary analysis indicates that this material is important for two reasons. First, individuals from the older time horizons are small in body size even relative to “pygmoid” populations from Southeast Asia and Indonesia, and thus may represent a marked case of human insular dwarfism. Second, while possessing a number of derived features that align them with Homo sapiens, the human remains from Palau also exhibit several skeletal traits that are considered to be primitive for the genus Homo. Significance These features may be previously unrecognized developmental correlates of small body size and, if so, they may have important implications for interpreting the taxonomic affinities of fossil specimens of Homo.
Translating microarray data for diagnostic testing in childhood leukaemia
Katrin Hoffmann, Martin J Firth, Alex H Beesley, Nicholas H de Klerk, Ursula R Kees
BMC Cancer , 2006, DOI: 10.1186/1471-2407-6-229
Abstract: We examined published microarray data from 104 ALL patients specimens, that represent six different subgroups defined by cytogenetic features and immunophenotypes. Using the decision-tree based supervised learning algorithm Random Forest (RF), we determined a small set of genes for optimal subgroup distinction and subsequently validated their predictive power in an independent patient cohort.We achieved very high overall ALL subgroup prediction accuracies of about 98%, and were able to verify the robustness of these genes in an independent panel of 68 specimens obtained from a different institution and processed in a different laboratory. Our study established that the selection of discriminating genes is strongly dependent on the analysis method. This may have profound implications for clinical use, particularly when the classifier is reduced to a small set of genes. We have demonstrated that as few as 26 genes yield accurate class prediction and importantly, almost 70% of these genes have not been previously identified as essential for class distinction of the six ALL subgroups.Our finding supports the feasibility of qRT-PCR technology for standardized diagnostic testing in paediatric ALL and should, in conjunction with conventional cytogenetics lead to a more accurate classification of the disease. In addition, we have demonstrated that microarray findings from one study can be confirmed in an independent study, using an entirely independent patient cohort and with microarray experiments being performed by a different research team.Acute lymphoblastic leukaemia (ALL) is a heterogeneous disease characterized by the presence of several subtypes that are of prognostic relevance. These subtypes can be distinguished based on immunophenotype, differentiation status, as well as chromosomal and molecular abnormalities. The identification of different ALL subtypes, the characterization of prognostic features, and the finding that ALL subtypes differ in their response to t
Hybrid wildebeest (Artiodactyla: Bovidae) provide further evidence for shared signatures of admixture in mammalian crania
Rebecca R. Ackermann,James S. Brink,Savvas Vrahimis,Bonita de Klerk
South African Journal of Science , 2010, DOI: 10.4102/sajs.v106i11/12.423
Abstract: The genus Connochaetes, Lichtenstein, 1814, contains two extant species, the blue wildebeest (C. taurinus, Burchell, 1823) and the black wildebeest (C. gnou, Zimmermann, 1780). In recent years, forced sympatry in confined areas within South Africa has led to interbreeding between these taxa and to fertile hybrid offspring. Here we report on a series of cranial characteristics of a hybrid wildebeest population culled at Spioenkop Dam Nature Reserve, KwaZulu-Natal, South Africa. Dental, sutural and horn morphological anomalies occur at high frequency within these animals. Similar cranial morphological anomalies have been shown in other mammalian hybrids and this study provides further evidence that such anomalies may characterise hybridisation more broadly across phylogenetically divergent mammalian groups, although the anomalies appear to differ in their expression across taxa. An increased ability to identify hybrids may also have important applications in the conservation of the endemic black wildebeest.
The estimation of herbage yields under fire and grazing treatments in the Mountain Zebra National Park
J. De Klerk,L.R. Brown,H. Bezuidenhout,G. Castley
Koedoe : African Protected Area Conservation and Science , 2001, DOI: 10.4102/koedoe.v44i1.181
Abstract: The application of fire as a management tool is often used to change the species composition of the vegetation and its cover to maintain plant communities in a specific successional stage. This study investigates the influence of two fire treatments (a head and a back fire) on the plateau grassland communities in the Mountain Zebra National Park (MZNP). The production of herbage yield on grazed areas and areas protected from grazing which were subjected to two fire treatments, were compared with that of an unburnt control area subjected to grazing in the same homogenous grassland over two growing seasons. No differences were found in herbage production between the two fire treatment areas. After the burn the grazing exclosures achieved the same herbage yield as the control area within two growing seasons. In comparison, the grazed areas could after the burn only achieve a herbage yield equal to 55.7 of that of the control area. The results indicate that fire stimulates active vegetation growth on the plateau grasslands in MZNP leading to a higher production rate and better utilisation by game.
Statistical adjustment of genotyping error in a case–control study of childhood leukaemia
Cooper Matthew N,de Klerk Nicholas H,Greenop Kathryn R,Jamieson Sarra E
BMC Medical Research Methodology , 2012, DOI: 10.1186/1471-2288-12-141
Abstract: Background Genotyping has become more cost-effective and less invasive with the use of buccal cell sampling. However, low or fragmented DNA yields from buccal cells collected using FTA cards often requires additional whole genome amplification to produce sufficient DNA for genotyping. In our case–control study of childhood leukaemia, discordance was found between genotypes derived from blood and whole genome amplified FTA buccal DNA samples. We aimed to develop a user-friendly method to correct for this genotype misclassification, as existing methods were not suitable for use in our study. Methods Discordance between the results of blood and buccal-derived DNA was assessed in childhood leukaemia cases who had both blood and FTA buccal samples. A method based on applying misclassification probabilities to measured data and combining results using multiple imputations, was devised to correct for error in the genotypes of control subjects, for whom only buccal samples were available, to minimize bias in the odds ratios in the case–control analysis. Results Application of the correction method to synthetic datasets showed it was effective in producing correct odds ratios from data with known misclassification. Moreover, when applied to each of six bi-allelic loci, correction altered the odds ratios in the logically anticipated manner given the degree and direction of the misclassification revealed by the investigations in cases. The precision of the effect estimates decreased with decreasing size of the misclassification data set. Conclusions Bias arising from differential genotype misclassification can be reduced by correcting results using this method whenever data on concordance of genotyping results with those from a different and probably better DNA source are available.
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