65 research outputs found
Facilitating Feature-Oriented Quality Assurance in Low-Maturity Variant-rich Systems
No full textContext: Many software systems exist in several variants customized for specific stakeholder requirements, such as different market segments or hardware constraints. This customization introduces a high level of complexity that renders traditional single-system quality assurance techniques inapplicable, since they need to consider variations and constraints between a system’s features—a.k.a feature-oriented or variability-aware analysis. While several analysis techniques have been conceived in the last two decades for this purpose, they mostly target a branch of variant-rich systems called software product lines, and are less applicable to systems that still rely on cloning strategies to engineer variants—a.k.a low-maturity variant-rich systems. Among other reasons, this is because such systems exhibit: immature architectures that do not systematically account for variability, redundancy that is not exploited to reduce analysis effort, and missing essential meta-information such as feature constraints and locations of features in source code.
Objective: This research aims to facilitate quality assurance in low-maturity variant-rich systems. Through analysis of the state-of-practice, we propose techniques that can improve maturity and help developers of such systems mitigate some challenges posed by redundancy.
Method: First, we conducted a survey and interviews with practitioners to identify industrial needs and practices for analyzing variant-rich systems, followed by a case study of some open source systems to understand where developers record information necessary for feature-oriented analysis. Then, we designed and systematically evaluated a technique and a tool that can improve the maturity of variant rich systems by supporting feature recording, and two techniques that can reduce analysis effort.
Results: Our results stem from two main contributions: our analysis of the state-of-practice and techniques we propose for improving maturity to facilitate feature-oriented analysis in low-maturity variant-rich systems. For the former, we present results of a survey and interviews targeting 27 practitioners from 18 companies in 8 countries to understand industrial practices and needs for analyzing variant-rich systems. Then, we present our empirical understanding of features and their characteristics (facets) based on a case study of two industrial open-source systems. For the latter, we present design decisions and an evaluation of a tool and technique that help developers proactively and continuously record features. Then, we present empirical data on the potential of two techniques for reducing QA effort: one for predicting software defects at the level of features (evaluated on 13 open-source systems), and another for propagating test cases across forked projects, i.e., projects with similar but cloned features (evaluated on over 426,000 test cases from 2,153 projects).
Conclusion: This thesis identifies the lack of adoption of feature-oriented quality assurance techniques in industry, and addresses the problem through tools and techniques for feature recording and quality assurance effort reduction
Early spatial and temporal validation of MODIS LAI product in the Southern Africa Kalahari
No full textWe evaluate the operational MODIS Leaf Area Index (LAI) product using field-sampled data collected at five sites in southern Africa in March 2000. One site (Mongu, Zambia) was sampled monthly throughout the year. All sites were along the International Geosphere Biosphere Programme's (IGBP) Kalahari Transect, which features progressively lower annual precipitation, and hence, lower vegetation productivity, from north to south. The soils are consistently sandy. At each site, we sampled the vegetation overstory along three 750-m transects using the Tracing Radiation and Architecture in Canopies (TRAC) instrument. The resulting plant area index values were adjusted with ancillary stem area data to estimate LAI. Despite some instrument characterization and production issues in the first year of MODIS operations, our results suggest the first-year MODIS LAI algorithm correctly accommodates structural and phenological variability in semiarid woodlands and savannas, and is accurate to within the uncertainty of the validation approach used here. Limitations of this study and its conclusions are also discussed.<br/
Vegetation structure characteristics and relationships of Kalahari woodlands and savannas
No full textThe Kalahari Transect is one of several International Geosphere–Biosphere Programme (IGBP) transects designed to address global change questions at the regional scale, in particular by exploiting natural parameter gradients (Koch et al., 1995). In March 2000, we collected near-synoptic vegetation structural data at five sites spanning the Kalahari's large precipitation gradient (about 300–1000 mm yr?1) from southern Botswana (?24°S) to Zambia (?15°S). All sites were within the expansive Kalahari sandsheet. Common parameters, including plant area index (PAI), leaf area index (LAI) and canopy cover (CC), were measured or derived using several indirect instruments and at multiple spatial scales. Results show that CC and PAI increase with increasing mean annual precipitation. Canopy clumping, defined by the deviation of the gap size distribution from that of randomly distributed foliage, was fairly constant along the gradient. We provide empirical relationships relating these parameters to each other and to precipitation. These results, combined with those in companion Kalahari Transect studies, provide a unique and coherent test bed for ecological modeling. The data may be used to parameterize process models, as well as test internally predicted parameters and their variability in response to well-characterized climatological differences.<br/
Evaluation of Olyset insecticide-treated nets distributed seven years previously in Tanzania.
No full textBACKGROUND: Insecticide-treated nets represent currently a key malaria control strategy, but low insecticide re-treatment rates remain problematic. Olyset nets are currently one of two long-lasting insecticidal nets recommended by WHO. An assessment was carried out of the effect of Olyset nets after seven years of use in rural Tanzania. METHODS: A survey of Olyset nets was conducted in two Tanzanian villages to examine their insecticide dosage, bioassay efficacy and desirability compared with ordinary polyester nets. RESULTS: Of 103 randomly selected nets distributed in 1994 to 1995, 100 could be traced. Most nets were in a condition likely to offer protection against mosquito biting. Villagers appreciated mainly the durability of Olyset trade mark nets and insecticide persistence. People disliked the small size of these nets and the light blue colour and preferred a smaller mesh size, features that can easily be modified. At equal price, 51% said they would prefer to buy an Olyset net and 49% opted for an ordinary polyester net. The average permethrin content was 33%-41% of the initial insecticide dose of 20,000 mg/Kg. Bioassay results indicated high knock-down rates at 60 minutes, but the mosquito mortality after 24 hours was rather low (mean: 34%). No significant correlation was found between bioassay results and insecticide concentration in and on the net. CONCLUSIONS: Olyset nets are popular, durable and with a much longer insecticide persistence than ordinary polyester nets. Hence, Olyset nets are one of the best choices for ITN programmes in rural malaria-endemic areas
Spatial and temporal variation of CO<sub>2</sub> efflux along a disturbance gradient in a <i>miombo</i> woodland in Western Zambia
No full textCarbon dioxide efflux from the soil surface was measured over a period of several weeks within a heterogeneous Brachystegia spp. dominated miombo woodland in Western Zambia. The objectives were to examine spatial and temporal variation of soil respiration along a disturbance gradient from a protected forest reserve to a cut, burned, and grazed area outside, and to relate the flux to various abiotic and biotic drivers. The highest daily mean fluxes (around 12 μmol CO2 m−2 s−1) were measured in the protected forest in the wet season and lowest daily mean fluxes (around 1 μmol CO2 m−2 s−1) in the most disturbed area during the dry season. Diurnal variation of soil respiration was closely correlated with soil temperature. The combination of soil water content and soil temperature was found to be the main driving factor at seasonal time scale. There was a 75% decrease in soil CO2 efflux during the dry season and a 20% difference in peak soil respiratory flux measured in 2008 and 2009. Spatial variation of CO2 efflux was positively related to total soil carbon content in the undisturbed area but not at the disturbed site. Coefficients of variation of efflux rates between plots decreased towards the core zone of the protected forest reserve. Normalized soil respiration values did not vary significantly along the disturbance gradient. Spatial variation of respiration did not show a clear distinction between the disturbed and undisturbed sites and could not be explained by variables such as leaf area index. In contrast, within plot variability of soil respiration was explained by soil organic carbon content. Three different approaches to calculate total ecosystem respiration (Reco) from eddy covariance measurements were compared to two bottom-up estimates of Reco obtained from chambers measurements of soil- and leaf respiration which differed in the consideration of spatial heterogeneity. The consideration of spatial variability resulted only in small changes of Reco when compared to simple averaging. Total ecosystem respiration at the plot scale, obtained by eddy covariance differed by up to 25% in relation to values calculated from the soil- and leaf chamber efflux measurements but without showing a clear trend
Spatial and temporal variation of CO&lt;sub&gt;2&lt;/sub&gt; efflux along a disturbance gradient in a &lt;i&gt;miombo&lt;/i&gt; woodland in Western Zambia
No full textAbstract. Carbon dioxide efflux from the soil surface was measured over a period of several weeks within a heterogeneous Brachystegia spp. dominated miombo woodland in Western Zambia. The objectives were to examine spatial and temporal variation of soil respiration along a disturbance gradient from a protected forest reserve to a cut, burned, and grazed area outside, and to relate the flux to various abiotic and biotic drivers. The highest daily mean fluxes (around 12 μmol m−2 s−1) were measured in the protected forest in the wet season and lowest daily mean fluxes (around 1 μmol m−2 s−1) in the most disturbed area during the dry season. Diurnal variation of soil respiration was closely correlated with soil temperature. The combination of soil water content and soil temperature was found to be the main driving factor at seasonal time scale. There was a 75% decrease in soil CO2 efflux during the dry season and a 20% difference in peak soil respiratory flux measured in 2008 and 2009. Spatial variation of CO2 efflux was positively related to total soil carbon content in the undisturbed area but not at the disturbed site. Coefficients of variation of efflux rates between plots decreased towards the core zone of the protected forest reserve. Normalized soil respiration values did not vary significantly along the disturbance gradient. Spatial variation of respiration did not show a clear distinction between the disturbed and undisturbed sites and was neither explained by soil carbon nor leaf area index. In contrast, within plot variability of soil respiration was explained by soil organic carbon content. Three different approaches to calculate total ecosystem respiration (Reco) from eddy covariance measurements were compared to two bottom-up estimates of Reco obtained from chambers measurements of soil- and leaf respiration which differed in the consideration of spatial heterogeneity. The consideration of spatial variability resulted only in small changes of Reco when compared to simple averaging. Total ecosystem respiration at the plot scale, obtained by eddy covariance differed by up to 25% in relation to values calculated from the soil- and leaf chamber efflux measurements but without showing a clear trend.
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Third-year students' preceptions of the use of ICT at a teacher training college in Namibia
No full textThesis (MPhil)--University of Stellenbosch, 2011.The use of ICT to enhance the quality of student learning is generally observable
in higher education institutions. The adoption of ICT policy for education in
Namibia in 1996 has profoundly encouraged the use of ICT to enhance student
learning at teachers training colleges, in particular Caprivi College of Education.
Although ICT has positioned itself in higher education, its implementation to
enhance student learning has been received with mixed feelings, attitudes and
perceptions among students.
The use of ICT in relation to learning paradigm, collaborative and/or co-operative
learning, deep learning approach and assessment seem to be problematic
among students and may affect their learning. Issues related to access to ICT,
ICT skills and support (technical and service) contribute to students’ negative
perceptions towards the use of ICT in learning.
The purpose of this study was to investigate students’ perceptions of the possible
effect of ICT application on student learning at Caprivi College of Education in
order to determine the ICT skills and learning strategies student teachers use to
enhance their learning.
The research strategy for this study was a quantitative survey. Quantitative data
was obtained by administering closed-ended questionnaires to third-year student
teachers at Caprivi College of Education. The study concludes that student
teachers overwhelmingly perceive the use of ICT to enhance their learning in
various ways.Master
Evaluation of the Long-Lasting Insecticidal Net Interceptor LN: Laboratory and Experimental Hut Studies against Anopheline and Culicine Mosquitoes in Northeastern Tanzania
No full textLong lasting insecticidal nets (LN) are a primary method of malaria prevention. Before new types of LN are approved they need to meet quality and efficacy standards set by the WHO Pesticide Evaluation Scheme. The process of evaluation has three phases. In Phase I the candidate LN must meet threshold bioassay criteria after 20 standardized washes. In Phase II washed and unwashed LNs are evaluated in experimental huts against wild, free flying anopheline mosquitoes. In Phase III the LN are distributed to households in malaria endemic areas, sampled over three years of use and tested for continuing insecticidal efficacy. Interceptor® LN (BASF Corporation, Germany) is made of polyester netting coated with a wash resistant formulation of alpha-cypermethrin. Interceptor LN was subjected to bioassay evaluation and then to experimental hut trial against pyrethroid-susceptible Anopheles gambiae and An. funestus and resistant Culex quinquefasciatus. Mosquito mortality, blood feeding inhibition and personal protection were compared between untreated nets, conventional alpha-cypermethrin treated nets (CTN) washed 20 times and LNs washed 0, 20 and 30 times. In Phase I Interceptor LN demonstrated superior wash resistance and efficacy to the CTN. In the Phase II hut trial the LN killed 92% of female An. gambiae when unwashed and 76% when washed 20 times; the CTN washed 20 times killed 44%. The LN out-performed the CTN in personal protection and blood-feeding inhibition. The trend for An. funestus was similar to An. gambiae for all outcomes. Few pyrethroid-resistant Cx. quinquefasciatus were killed and yet the level of personal protection (75-90%) against Culex was similar to that of susceptible An. gambiae (76-80%) even after 20 washes. This protection is relevant because Cx. quinquefasciatus is a vector of lymphatic filariasis in East Africa. After 20 washes and 60 nights’ use the LN retained 27% of its initial insecticide dose. Interceptor LN meets the approval criteria set by WHO and is recommended for use in disease control against East African vectors of malaria and filariasis. Some constraints associated with the phase II evaluation criteria, in particular the washing procedure, are critically reviewed
Precipitation as driver of carbon fluxes in 11 African ecosystems
No full textThis study reports carbon and water fluxes between the land surface and atmosphere in eleven different ecosystems types in Sub-Saharan Africa, as measured using eddy covariance (EC) technology in the first two years of the CarboAfrica network operation. The ecosystems for which data were available ranged in mean annual rainfall from 320 mm (Sudan) to 1150 mm (Republic of Congo) and include a spectrum of vegetation types (or land cover) (open savannas, woodlands, croplands and grasslands). Given the shortness of the record, the EC data were analysed across the network rather than longitudinally at sites, in order to understand the driving factors for ecosystem respiration and carbon assimilation, and to reveal the different water use strategies in these highly seasonal environments.
Values for maximum net carbon assimilation rates (photosynthesis) ranged from −12.5 μmol CO2 m−2 s−1 in a dry, open Millet cropland (C4-plants) up to −48 μmol CO2 m−2 s−1 for a tropical moist grassland. Maximum carbon assimilation rates were highly correlated with mean annual rainfall (r2=0.74). Maximum photosynthetic uptake rates (Fpmax) were positively related to satellite-derived fAPAR. Ecosystem respiration was dependent on temperature at all sites, and was additionally dependent on soil water content at sites receiving less than 1000 mm of rain per year. All included ecosystems dominated by C3-plants, showed a strong decrease in 30-min assimilation rates with increasing water vapour pressure deficit above 2.0 kPa
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