The Lateral Torsional Buckling Strength of Cold-formed Stainless Steel Beams

The findings of an investigation of the lateral torsional buckling strength of cold-formed stainless steel beams are reported in this study. The sections under consideration are cold-formed lipped channel sections spot-welded back to back to form doubly-symmetric lipped I-beams. The beams were fabricated from a modified AISI Type 409 stainless steel, designated Type 3CR12 corrosion resisting steel. The purpose of this study is to compare the experimental lateral torsional buckling strengths of doubly-symmetric beams to the theoretical predictions proposed by the ASCE Specification for the Design of Cold-Formed Stainless Steel Structural Members. It was concluded in this investigation that an acceptable prediction of beam strength may be obtained through the use of the tangent modulus approach adopted in the ASCE stainless steel design specification

The Lateral Torsional Buckling Strength of Cold-formed Stainless Steel Lipped Channel Beams

The findings of an investigation into the lateral buckling strength of cold-formed singly-symmetric stainless steel beams are reported in this study. The singly-symmetric sections under consideration were lipped channel sections fabricated from a modified AISI stainless steel Type 409 designated 3CR12, a ferritic corrosion resisting steel. The purpose of this study was to compare the experimental strengths of singly-symmetric sections to the theoretical predictions proposed by the new ASCE Specification for the Design of Cold-Formed Stainless Steel Structural Members. It was concluded in this investigation that the tangent modulus approach adopted in the design specification for stainless steels, compared well with the experimental results

The effects of elephants and fire on vegetation at Marakele National Park, South Africa

Elephants and fire can modify African savanna ecosystems. The authors evaluated the influence that elephants and fires had on five mountainous plant communities in Marakele National Park. These plant communities were surveyed from 1996 to 2010 with the first sampling in 1996 in the absence of elephants. Initially thirty-nine elephants, introduced in 1996, increased to 150 by 2010 while fires occurred roughly every second year. Over this period vegetation changed and in four of the five cases these associated with structural damage indices, assumed to reflect the effects of elephants. Fire played a role in one of the five mountainous plant communities. The expansion of areas available for elephants partially resulted in halting vegetation changes. The authors conclude that existing resource gradients still impose intensity of use by elephants that can degrade plant communities. In some instances elephant disturbance may facilitate fire disturbance in future. The management should focus on restoring spatial and temporal limitation of resource gradients such as water, and on how elephants use landscapes, while protecting unique plant communities in the interim.Les éléphants et l’incendie peuvent modifier les écosystèmes de la savane africaine. Les auteurs ont évalué l’influence des éléphants et des incendies sur cinq communautés de plantes montagneuses dans le parc national Marakele. On a étudié ces communautés végétales de 1996 à 2010 avec le premier échantillonnage fait en 1996 en l’absence des éléphants. A l’origine, trente-neuf éléphants, introduits en 1996, se sont multipliés jusqu’à 150 en 2010 alors que les incendies se produisaient approximativement tous les deux ans. Au cours de cette période, la végétation a changé et, dans quatre cas sur cinq, ceux associés aux indices de dommages structurels semblaient refléter les effets des éléphants. L’incendie a joué un rôle dans l’une des cinq communautés de plantes montagneuses. L’expansion des zones disponibles pour les éléphants a entraîné en partie l’arrêt des changements de végétation. Les auteurs concluent que les gradients de ressources existants imposent toujours une intensité d’utilisation par les éléphants qui peuvent dégrader les communautés végétales. Dans certains cas, la perturbation par les éléphants peut faciliter celle de l’incendie à l’avenir. La gestion devrait se concentrer sur la restauration de la limitation spatiale et temporelle des gradients de ressources, comme l’eau, et sur la façon dont les éléphants utilisent les paysages tout en protégeant les communautés végétales uniques dans l’entre-temps.http://www.pachydermjournal.org/index.php/pachy/indexam2018Plant Production and Soil Scienc

Plant communities of the Soutpansberg Arid Northern Bushveld

The Soutpansberg Arid Northern Bushveld is one of eight major vegetation types (MVT) described for the Soutpansberg-Blouberg region. The plant communities of this MVT are described in detail. Main ecological drivers of the vegetation structure and species composition of these communities are discussed and some conservation recommendations are made. Phytosociological data from a subset of 72 Braun-Blanquet sample plots collected in the Soutpansberg Arid Northern Bushveld were classifi ed using Two-way Indicator Species Analysis (TWINSPAN) and ordinated using a Detrended Correspondence Analysis (DECORANA). The resulting classifi cation was further refi ned with table-sorting procedures based on the Braun-Blanquet fl oristic-sociological approach to vegetation classifi cation using the computer software MEGATAB and JUICE. Eight plant communities were identifi ed and described as Commiphora tenuipetiolata-Adansonia digitata short open woodland, Ledebouria ovatifolia-Commiphora mollis short bushland, Phyllanthus reticulatus- Acacia nigrescens short bushland, Tinnea rhodesiana-Combretum apiculatum short bushland, Dichrostachys cinerea subsp. africana-Spirostachys africana low thickets, Themeda triandra-Pterocarpus rotundifolius short closed grassland on steep basaltic slopes, Cyperus albostriatus-Syzygium cordatum sandveld wetlands, and Sesamothamnus lugardii-Catophractes alexandri tall sparse shrubland. These plant communities are event-driven ecosystems, predominantly infl uenced by frequent droughts, exposure to desiccation and unpredictable rainfall events. The complex topography of the Soutpansberg further contributes to the aridity of these ecosystems. The classifi cation and ordination analyses show similar groupings in the vegetation of the Soutpansberg Arid Mountain Bushveld. This confi rms the usefulness of complimentary analysis, using both classifi cation and ordination methods on a single data set in order to examine patterns and to search for group structure. CONSERVATION IMPLICATIONS: The results from this study will alter existing regional vegetation maps profoundly. The described plant communities of these arid event-driven ecosystems should be used as benchmark examples of the region’s primary vegetation. Conservation and management planning should be based on these vegetation units.The National Research Foundationhttp://www.koedoe.co.zaam201

A reclassification and description of the Waterberg mountain vegetation of the Marakele National Park, Limpopo province, South Africa

The description and classification of vegetation are important for conservation and resource management. The aim of this study was to identify, reclassify and describe the plant communities present in the Waterberg Mountain vegetation of the Marakele National Park in the Limpopo province, South Africa. A phytosociological classification, mapping and description of sections of the Waterberg Mountain vegetation in the park were done in 1995. Since 1995, various farms adjacent to the park have been bought and incorporated into it. Little is known about the vegetation and habitat status of these newly acquired areas, which led to this study. The floristic data were analysed according to the Braun-Blanquet procedure using the Braun Blanquet Personal Computer (BBPC) suite as well as the JUICE software package, whilst the diversity of the plant communities was determined using the Shannon–Wiener and Gini–Simpson indices. A total of 12 plant communities were identified and are described according to their diagnostic, constant and dominant plant species as determined from the synoptic table analysis as well as their characteristic species as derived from the phytosociological table. Based on the topography and plant species composition, the vegetation can be grouped into five major groups, namely the: (1) lower midslope and plateau shrub- and woodlands, (2) high altitude midslope woodland, (3) high-lying plateau and midslope grass-, shrub- and woodlands, (4) ravine, footslope and drainage line forests and woodland, and (5) higher-lying plateau wetlands and forblands. The high altitude midslope grassland and shrubland and the lower midslope and plateau areas have the highest diversity. The high-lying vegetation has affinity with Bankenveld and Drakensberg vegetation, whilst the relatively low-lying plateaus and midslope vegetation are typical of the bushveld areas. CONSERVATION IMPLICATIONS : This reclassification, mapping and description of the Waterberg Mountain vegetation have been incorporated into the Management Plan for the park. It will enable managers to make scientifically based decisions on the management of the different ecosystems to ensure biodiversity conservation. This vegetation study also provides baseline information that allows for vegetation assessments to determine veld condition, carrying capacity and stocking density for the park.The University of South Africa (UNISA) and SANParks.http://www.koedoe.co.zaam2022Plant Production and Soil Scienc

The influence of fire on rodent abundance at the N'washitshumbe enclosure site, Kruger National Park, South Africa

The relative population numbers of rodents were studied in nine habitats in and outside the N’washitshumbe enclosure site, Kruger National Park, before and after burning the firebreaks that surround the enclosure. Trap success was exceptionally high, and the field work is suspected to have coincided with a Mastomys population explosion. This genus dominated the small mammal communities before and after the burn, and never disappeared from the burnt patches. Its numbers also did not crash directly after the burn, as have been reported in most other studies. Movement from the burnt areas was observed, which may have had a significant impact on the numbers of rodents caught both inside the enclosure and in the more natural areas outside. Our study suggests that fire can be investigated as a tool to keep rodent densities down in areas where they are nuisance animals, especially when used in conjunction with models that forecast outbreaks of Mastomys. It also emphasizes the value of long-term studies informing management strategies for animal damage control and biodiversity and ecosystem conservation.http://www.bioone.org/loi/afzoab201

Foxn1 Regulates Lineage Progression in Cortical and Medullary Thymic Epithelial Cells But Is Dispensable for Medullary Sublineage Divergence

The forkhead transcription factor Foxn1 is indispensable for thymus development, but the mechanisms by which it mediates thymic epithelial cell (TEC) development are poorly understood. To examine the cellular and molecular basis of Foxn1 function, we generated a novel and revertible hypomorphic allele of Foxn1. By varying levels of its expression, we identified a number of features of the Foxn1 system. Here we show that Foxn1 is a powerful regulator of TEC differentiation that is required at multiple intermediate stages of TE lineage development in the fetal and adult thymus. We find no evidence for a role for Foxn1 in TEC fate-choice. Rather, we show it is required for stable entry into both the cortical and medullary TEC differentiation programmes and subsequently is needed at increasing dosage for progression through successive differentiation states in both cortical and medullary TEC. We further demonstrate regulation by Foxn1 of a suite of genes with diverse roles in thymus development and/or function, suggesting it acts as a master regulator of the core thymic epithelial programme rather than regulating a particular aspect of TEC biology. Overall, our data establish a genetics-based model of cellular hierarchies in the TE lineage and provide mechanistic insight relating titration of a single transcription factor to control of lineage progression. Our novel revertible hypomorph system may be similarly applied to analyzing other regulators of development

Guidelines for phytosociological classifications and descriptions of vegetation in southern Africa

Changes in the environment are first observed in changes in the vegetation. Vegetation survey, classification and mapping form the basis on which informed and scientifically defendable decisions on the environment can be taken. The classification and mapping of vegetation is one of the most widely used tools for interpreting complex ecosystems. By identifying different plant communities we are essentially identifying different ecosystems at a particular hierarchical level. Phytosociologists in Europe have been involved in such studies following, in particular, the Braun-Blanquet approach since the early 1900s. In South Africa, such studies were undertaken on a limited basis from the early 1970s and have since then steadily increased. The surveying of the enormous diversity of South African vegetation is one of the objectives of phytosociological studies. The demand for such data has steadily increased over the past few years to guide conservation policies, biodiversity studies and ecosystem management. In South Africa, numerous publications on the vegetation of conservation and other areas in the different biomes have been produced over the last few decades. However, vegetation scientists in South Africa experience unique problems. The purpose of this article is therefore to provide an overview of the history and the specific focus of phytosociological studies in South Africa and to recommend minimum requirements and methods to be followed when conducting such studies. It is believed that the incorporation of these requirements will result in scientifically justifiable research of high quality by phytosociologists in South Africa. CONSERVATIOM IMPLICATIONS: Effective conservation cannot be obtained without a thorough knowledge of the ecosystems present in an area. Consistent vegetation classifications and descriptions form the basis of conservation and monitoring exercises to maintain biodiversity. The incorporation of these guidelines and requirements will facilitate quality phytosociological research in South Africa.http://www.koedoe.co.zaam201