Towards an option space for network structures in computer-based instruction

There are three major agents in a computer-based instruction (CBI) environment: the tutor, the tutoring system and the tutee. The emphasis of this paper is on the tutoring system which contains the instructional content and structures for presenting the content, the rules guiding a particular student's path through the material, and information regarding the performance data to be recorded. A CBI program consists of a network of related chunks of information, called nodes, that are connected by means as associated links. Research has been undertaken into the general structures of a CBI environment and some of of the results will be discussed in this paper. The structure that makes up a CBI program is essential a directed semantic multigraph. Formal specifications are employed to discuss several properties that influence the usability of these CBI networks structures, including reachability, determinism, precedence ordering and restartability. Although these structures are discussed in the context of CBI, the particular properties can also be transferred to other multimedia applications

A deep photometric survey of the Abell cluster SO423 : a pilot study for the UCT SALT supercluster survey

Includes bibliographical references (leaves 99-101)

Investigating Long-Term Behaviour of X-ray Binaries Using Archival Data

Long term modulations have been detected in a wide variety of both low and high-mass X-ray binaries. The All Sky Monitor on board the Rossi X-ray Timing Explorer provides the most extensive (~15 years) and sensitive X-ray archive for studying such behaviour. Since those variations were often intermittent and/or aperiodic, we used a time-dependent Dynamic Power Spectrum method to examine how the modulations themselves vary with time in a systematic way. Some were found to be remarkably stable, while others show a range of properties, from even longer variability time-scales to quite chaotic behaviour

Risk factors associated with the intervention of perpetrators of domestic violence

INTRODUCTION: South Africa has the highest incidence of violence against women and a woman is killed every six hours by an intimate partner. Furthermore, women in South Africa are more likely to be killed by an intimate partner than a stranger. It seems apparent that not much is known about the men who will continue to use violence in an intimate relationship or those who would kill their partners. International trends have indicated that intervention with either the survivor or the batterer in isolation is futile and greater recognition has been given to the development of comprehensive and co-ordinated responses. These co-ordinated responses must include community, social as well as criminal justice interventions. Yet, intervention programmes for batterers are in their infancy in Africa, with a special interest developing really only over the last five years. The initial development of any intervention for batterers emerged from the observation that the beatings or killings did not stop simply because the survivor received an intervention. Yet the batterer programmes that developed were not always in the best interest or safety of the women. METHODS: This study used the methodological framework of intervention research and design to develop a technology for intervening with the batterer himself. The different phases of this methodological framework was used to analyse the problem, gather and synthesize information through a literature review, study functional elements of successful batterer intervention programmes and then to design a risk-based assessment and intervention guidelines. The writer implemented an existing risk assessment guide, called the Spousal Assault Risk Assessment guide (SARA) to this end and the outcomes informed the design of the framework. The writer used purposive sampling to include the 53 male respondents and 47 female respondents in this study. RESULTS: The main findings of this study concur with the overall trends reflected in literature on domestic violence and the management of batterers. The implementation of the SARA guidelines further confirmed that treatment providers must assess batterers very thoroughly prior to the commencement of batterer intervention programmes. The identification of risk markers must clearly be taken into consideration when programmes are developed to manage the batterer as a means to stop ongoing domestic violence. Specific findings that emerged from the different phases of the research methodology are presented in greater detail in this final research report. CONCLUSIONS: The findings of this study concur with the main trends detected in the literature regarding the risk markers for continued violence. Batterers who have a history of violence, were exposed to violence during childhood, are impulsive and present with poor anger management skills appear to continue using intimate violence. Those men who tend to ignore or violate protection orders and restraining orders also appear to be more committed to using continued intimate violence

Studying the environmental dependence of star formation properties of galaxies in the Abell 1437 galaxy cluster and its surrounding large scale structure

Includes bibliographical references.It has become clear that the local galaxy environment plays a crucial role in the evolution of galaxies. Recent studies show a strong bimodal distribution of galaxy properties, with red, passive galaxies dominating the bimodal distribution in dense environments, compared to blue, actively star forming galaxies dominating the bimodal distribution in low density environments. Blue, star-forming galaxies are continuously transformed into red, passive galaxies through one or more processes while being accreted into higher density environments. The processes responsible for the observed transformation remain uncertain. We address these issues by performing an in-depth study of large-scale structure surrounding the galaxy cluster Abell 1437 at z = 0.135. We consider the colour and specific star formation rate distributions of galaxies as a function of environment. In this thesis we develop techniques to derive environmental samples which consist of a cluster, groups, filament and field. The large-scale structure surrounding the cluster is characterised through the use of a Friends-of-Friends algorithm based on spectroscopic data. This provides a reference from which we construct a photometric environmental catalogue using methods developed to find groups and define filamentary structure. To accomplish this, we construct a ugrizJHK multi-band dataset using a custom pipeline to derive a seeing matched photometric catalogue from Sloan Digital Sky Survey (SDSS) and UKIRT Deep Sky Survey (UKIDSS) imaging data. The photometric dataset is complemented by a near uniformly sampled spectroscopic dataset from the SDSS and Two Degree Field (2dF) survey. Stellar masses and star formation rates for the environmental samples are derived using the state-of-the-art magphys SED fitting code. The environmental samples we derive yield, within the uncertainties, similar galaxy populations than typically found in clusters, groups and the field. Red fractions were computed for the cluster, groups, filament and field sample for which we found 0.90 ± 0.13, 0.79 ± 0.01, 0.69 ± 0.02 and 0.58 ± 0.01 respectively. This is the first filament red fraction measurement made in this way. We studied the passive fraction of galaxies as a function of environment using specific star formation rates. Passive fractions were computed using two different definitions of passiveness, 1/tH (log(sSFR) = −10.07) and the minimum in the bimodal sSFR distribution (log(sSFR) = −11.0) as the division between active and passive galaxies. We found that the log(sSFR) = −11.0 bimodal divider is a natural division between active and passive galaxies and does not suffer from density-dependent selection effects. Quiescent fractions derived from the environmental samples reproduce previously known trends of star formation rates with environment. The filament environment is one of the least well studied environments since their low galaxy density makes them difficult to detect. We studied the fractional excess of star forming galaxies along the filament between Abell 1437 and the neighbouring region of overdensities, and find a significant increase in star formation activity. Although there have been hints of excess star formation in filaments previously, we claim our results to be of highest significance thus far

Studying the environmental dependence of star formation properties of galaxies in the Abell 1437 galaxy cluster and its surrounding large scale structure

Includes bibliographical references.It has become clear that the local galaxy environment plays a crucial role in the evolution of galaxies. Recent studies show a strong bimodal distribution of galaxy properties, with red, passive galaxies dominating the bimodal distribution in dense environments, compared to blue, actively star forming galaxies dominating the bimodal distribution in low density environments. Blue, star-forming galaxies are continuously transformed into red, passive galaxies through one or more processes while being accreted into higher density environments. The processes responsible for the observed transformation remain uncertain. We address these issues by performing an in-depth study of large-scale structure surrounding the galaxy cluster Abell 1437 at z = 0.135. We consider the colour and specific star formation rate distributions of galaxies as a function of environment. In this thesis we develop techniques to derive environmental samples which consist of a cluster, groups, filament and field. The large-scale structure surrounding the cluster is characterised through the use of a Friends-of-Friends algorithm based on spectroscopic data. This provides a reference from which we construct a photometric environmental catalogue using methods developed to find groups and define filamentary structure. To accomplish this, we construct a ugrizJHK multi-band dataset using a custom pipeline to derive a seeing matched photometric catalogue from Sloan Digital Sky Survey (SDSS) and UKIRT Deep Sky Survey (UKIDSS) imaging data. The photometric dataset is complemented by a near uniformly sampled spectroscopic dataset from the SDSS and Two Degree Field (2dF) survey. Stellar masses and star formation rates for the environmental samples are derived using the state-of-the-art magphys SED fitting code. The environmental samples we derive yield, within the uncertainties, similar galaxy populations than typically found in clusters, groups and the field. Red fractions were computed for the cluster, groups, filament and field sample for which we found 0.90 ± 0.13, 0.79 ± 0.01, 0.69 ± 0.02 and 0.58 ± 0.01 respectively. This is the first filament red fraction measurement made in this way. We studied the passive fraction of galaxies as a function of environment using specific star formation rates. Passive fractions were computed using two different definitions of passiveness, 1/tH (log(sSFR) = −10.07) and the minimum in the bimodal sSFR distribution (log(sSFR) = −11.0) as the division between active and passive galaxies. We found that the log(sSFR) = −11.0 bimodal divider is a natural division between active and passive galaxies and does not suffer from density-dependent selection effects. Quiescent fractions derived from the environmental samples reproduce previously known trends of star formation rates with environment. The filament environment is one of the least well studied environments since their low galaxy density makes them difficult to detect. We studied the fractional excess of star forming galaxies along the filament between Abell 1437 and the neighbouring region of overdensities, and find a significant increase in star formation activity. Although there have been hints of excess star formation in filaments previously, we claim our results to be of highest significance thus far

Population structure of a non-breeding colony of the cape fur seal arctocephalus pusillus pusillus at Cape Frio, Namibia

The age and sex composition at a large non-breeding colony of the Cape fur seal Arctocephalus pusillus pusillus at Cape Frio, Namibia, are described. A ground estimate indicated that there were approximately 20 000 seals of all age groups and of both sexes at the colony during September 1989, around two months before the pupping season. The sex ratio of seals sampled was 1.61 : 1 (n = 107, 61.7% male). Most of the males were immature, 2- and 3-year-olds, although some older, mature bulls were present at the colony. In contrast, only 9.8% of females were sexually immature and 80.5% were older than 13 years. None of the young females was reproductively active and older females had reduced reproductive rates. Reproductive status of females differed from that of seals at other breeding colonies