Volume 26, Issue 3, 2007
Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie - Volume 26, Issue 3, September 2007
Volume 26, Issue 3, September 2007
Visuele interpretasie van ASTER-satellietdata, deel I : geologiese kartering in die Wieg van die Mensdomwêrelderfenisgebied
Authors: H.J. Van Niekerk and L.A. Sandham
Source: Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie 26, pp 177 –195 (2007)
Satelliet-afstandwaarneming het 'n kragtige instrument in die geowetenskaplike navorsingsarsenaal geword sedert die eerste van die aard-observasiesatelliete in 1972 gelanseer is, maar die effektiwiteit daarvan is egter ontoereikend as gevolg van die beperkte spektrale en ruimtelike sensitiwiteit. Op 18 Desember 1999 is die Terra-platform in bedryf gestel met vyf afstandwaarnemingsinstrumente, onder andere ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer). ASTER bestaan uit drie afsonderlike instrument-substelsels, wat met behulp van aparte optiese stelsels elk in 'n ander spektrale domein funksioneer, naamlik die Sigbare en Baie Naby-Infrarooi substelsel met 15m-ruimtelike resolusie, die Kortgolf-Infrarooi substelsel met 30m-ruimtelike resolusie en die Termiese-Infrarooi substelsel met 90m-ruimtelike resolusie. ASTER bied beter spektrale resolusie en ruimtelike resolusie as Landsat MSS, Landsat TM, Landsat ETM+ en SPOT. Hierdie artikel doen verslag oor die verbeterde kartering van litostratigrafie, geologiese strukture en mynbouverwante verskynsels wat met die visuele interpretasie van verwerkte ASTER-satellietbeelde behaal is. Die verbeterde kartering in die Wieg van die Mensdom-wêrelderfenisgebied bevestig die potensiaal van ASTER-satellietdata vir verdere toepassings deur geowetenskaplikes.
Habitatsvoorkeure, voedafstande en vliegrigtings van vee-reiers (Bubulcus ibis) in die sentrale Vrystaat
Source: Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie 26, pp 196 –204 (2007)
Habitat preference, feeding distance and flight direction of cattle egrets (Bubulcus ibis) in the central Free State.
In the Free State, two thirds of all actively feeding cattle egrets (Bubulcus ibis) were observed in open grassland habitats. If the birds that fed in association with hosts are considered separately, the dominance of grassland, especially short grass, is even higher. By contrast, cattle egrets that fed independently of hosts showed a clear preference for tall grass and edges of water body. Marked differences in habitat use between cattle egrets that fed in the presence or absence of hosts even occurred on a temporal basis during the course of the day. More than three quarters (78,6%) of all cattle egrets observed in the vicinity of the Soetdoring Nature Reserve fed within a radius of 15 km of the breeding colony. Depending on the time of the year, significant changes occurred in the general flight direction from and to the colony. Positive correlations were obtained between the outward and return flights, but not between the general flight direction and prevailing wind direction.
In die Vrystaat is twee derdes van alle aktief voedende vee-reiers (Bubulcus ibis) in oop grasveldhabitats waargeneem. Indien die voëls wat in assosiasie met gashere voed afsonderlik beskou word, is die dominansie van grasveld, en veral kort gras, selfs hoër. Hierteenoor toon vee-reiers wat onafhanklik van gashere voed 'n duidelike voorkeur vir lang gras en damoewers as voedingshabitat. Opvallende verskille in habitatsbenutting tussen vee-reiers wat in die teenwoordigheid of afwesigheid van gashere voed, kom selfs op 'n temporele basis gedurende die loop van die dag voor. Meer as driekwart (78,6%) van alle vee-reiers wat in die omgewing van die Soetdoring Natuurreservaat waargeneem is, het binne 'n radius van 15 km vanaf die broeikolonie gevoed. Afhangende van die tyd van die jaar het opvallende veranderings in die algemene vliegrigting vanaf en na die broeikolonie plaasgevind. Positiewe korrelasies tussen die uitwaartse en terugkerende vlugte is verkry, maar nie tussen die algemene vliegrigting en heersende windrigting nie.
Die kardiovaskulêre stelsel soos in die antieke tyd verstaan
Source: Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie 26, pp 205 –215 (2007)
The cardiovascular system, as understood in antiquity
Cardiovascular concepts in antiquity were primitive up to the early 5th century BC, when Greek philosopher-physicians like Empedocles and Diogenes divorced human physiology from its previous magico-religious base in order to find answers in the natural sciences. The heart was not initially seen as central to the cardiovascular system - blood (containing life-giving pneuma) moved through the body in blood vessels (phlebes) by way of a spontaneous "ebb and flow" motion. Their perceived anatomical vascular models were quite fanciful, but nevertheless accepted by the Hippocratic doctors, who, except for a single work, The heart (containing a useful description of the heart), added little of significance to the subject. Based on animal dissections, post-Hippocratic authors like Diocles and Praxagoras first distinguished between arteries and veins, confirmed that the heart had two main chambers (ventricles) and extended the theory that "innate heat" in the left ventricle produced pneuma which filled the arteries; only veins contained blood, produced in the right ventricle. Basing their theories on human dissections the Alexandrians, Herophilus and Erasistratus (3rd century BC) produced the first accurate descriptions of the heart and major components of the vascular system. Erasistratus even postulated minute (normally non-functional) peripheral arterio-venous anastomoses. The heart' pump function was only partially understood - diastole was seen as the active phase of the cardiac cycle (sucking blood into the heart), and the pulse as inherent contraction of the arterial wall. After Herophilus and Erasistratus human dissection ceased, putting an end to further significant developments in unravelling the cardiovascular system. In the 2nd century AD, Celsus consolidated known knowledge, even adding minor contributions (e.g. a description of the coronary vessels) based on his own animal dissections. He mainly confirmed the Alexandrians' findings and contemporary views on cardiac function, including inherent arterial pulsation, "ebb and flow" blood movement in veins, and the existence of pneuma. He claimed that arteries contained blood, not pneuma. These views, as well an erroneous personal contribution (that there were minute pores in the heart's interventricular septum), remained medical dogma throughout the Middle Ages up to the Renaissance.
Kennis van die kardiovaskulêre stelsel het in die antieke tyd sentraal gestaan in die soeke na begrip van menslike fisiologie en optimale gesondheid. Vervleg in vele wanbegrippe, onder andere oor waar die liggaam se hooforgaan (hegemonikon) geleë was, die rol van 'n lewegewende substans (pneuma) en die sogenaamde inherente hitte van die hart, het 'n omvattende begrip van die hart en bloedvatstelsel traag ontwikkel. In hierdie studie word die groei van kennis omtrent die kardiovaskulêre stelsel vanaf die vroegste tyd tot en met die einde van die Romeinse era (5de eeu n.C.) ondersoek.
Die opleiding van persone uit benadeelde groepe in rekenaargebruik : is die agterstand nie té groot om te oorbrug nie?
Authors: P.J. Blignaut, E.H. Dednam and T.R. Beelders
Source: Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie 26, pp 216 –235 (2007)
Training people from disadvantaged groups in computer use : Is the backlog not too big to overcome?
The digital divide is both a matter of having access to technology and being able to use it. There are several initiatives to roll out Information and Communication Technology (ICT) in public places in South Africa, but the question arises as to whether people will be able to use it effectively. Is the backlog with regard to general education and training not so insurmountable that people from disadvantaged communities are not educable for computer usage?
This paper reports on the experiences and observations of instructors during a word processing training course for people from such communities. An interaction model that incorporates user and interface limitations with the difficulties experienced, serves as framework for the discussion. It became clear that most of the difficulties that attendees experienced were related to lack of technological experience, a limitation that can be eliminated through practice and perseverance. Enough practice might also result in an attenuation of the effects of some psychological limitations.
Die digitale onderskeid is tegelyk 'n kwessie van toegang tot tegnologie en die vermoë om dit te gebruik. Daar bestaan verskeie inisiatiewe om Inligtings- en Kommunikasietegnologie (IKT) in openbare plekke in Suid-Afrika te plaas, maar die vraag ontstaan of mense in staat sal wees om dit doeltreffend te gebruik. Is die agterstand met betrekking tot algemene onderwys en opleiding nie so groot dat mense van benadeelde gemeenskappe nie in rekenaargebruik opleibaar is nie?
Hierdie artikel is 'n weergawe van die ervaring en waarnemings van instrukteurs gedurende 'n opleidingskursus in woordverwerking vir persone uit sulke gemeenskappe. 'n Interaksiemodel wat gebruikers- en koppelvlakbeperkinge in verband bring met die struikelblokke wat dit tot gevolg het, dien as raamwerk vir die bespreking. Dit is duidelik dat die meeste struikelblokke wat kursusgangers ervaar het, hulle oorsprong in gebrekkige blootstelling aan tegnologie het - 'n beperking wat met oefening en deursettingsvermoë oorkom kan word. Genoegsame oefening kan ook sommige van die effekte van die sielkundige en kognitiewe beperkinge, soos rekenaarangs, navigasieprobleme en konseptualisering van hiërargieë, verlig. Genoeg blootstelling kan ook daartoe lei dat 'n gebruiker konsepte begin verstaan wat nie in sy/haar moedertaal verduidelik kan word nie.
Op koers met Suid-Afrikaanse universiteite? : point of view
Author Johann R.E. Lutjeharms
Source: Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie 26, pp 237 –238 (2007)