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Journal of the National Science Foundation of Sri Lanka
Journal Prestige (SJR): 0.157
Number of Followers: 2  

  This is an Open Access Journal Open Access journal
ISSN (Print) 1391-4588
Published by Sri Lanka Journals Online Homepage  [48 journals]
  • Rediscovery of Tetragonula praeterita after 1860: an unremarked common
           stingless bee endemic to Sri Lanka

    • Abstract: Three species of stingless bees are documented from Sri Lanka, namely, Tetragonula iridipennis (Smith), Lisotrigona cacciae (Nurse) and the endemic Tetragonula praeterita (Walker). Tetragonula irdipennis is the well-known, widely distributed stingless bee in Sri Lanka while L. cacciae is a recent record of a tear drinking stingless bee from a single site in Sri Lanka. Until the recent rediscovery, T. praeterita was known only from its type specimen deposited in the British Natural History Museum, London with Sri Lanka as its locality and 1860 as its date of description. Location of several stingless bee nests, with an entrance different to that of the well-known T. iridipennis, led to the re-discovery of T. praeterita. Its nesting sites, characteristics of the nest entrance tube and the morphological and morphometric differences of the worker caste compared to those of T. iridipennis are presented in the paper. Eight species of stingless bees have been reported from the Indian subcontinent. It is possible that more than three species of stingless bees occur in Sri Lanka. Published on 2018-03-28 05:34:22
       
  • An efficient algorithm to calculate relative permittivity from
           multi-layered stripline based measurements at microwave frequencies

    • Abstract: In recent years, multi-layer stripline or microstrip line based dielectric measurement has drawn the attention of many researchers. These methods are particularly attractive as they can readily be used for the dielectric measurement of non-metal clad material. Measurement setups developed using the multi-layer approach have the added advantage that they need very little sample preparation. However, the extraction of dielectric properties in these experimental setups is complex due to the multi-layer nature of the problem. At present, this is usually done using brute-force approaches, which take long computational times and large memory. This paper presents an efficient technique based on the Newton Raphson algorithm to address this. The algorithm developed is coded in Matlab and the results show a significant improvement over the brute-force method. Published on 2018-03-28 05:32:47
       
  • Use of Mandel’s bundle of lines model to improve agreement of a
           panel of tea tasters

    • Abstract: Sensory evaluation is of prime importance in the tea industry. The price of tea is predominantly determined by the tea taster’s judgement. Hence, statisticians and sensory analysts have significant interest in improving the reliability of sensory panel evaluations. This study suggests a statistical de-biasing approach to improve the agreement of panels of tea tasters by using the Mandel’s bundle of lines model. This paper analyses data from a panel of eight experts who evaluated 72 black tea samples collected from 13 different geographical regions of Sri Lanka over a one year (January 2010 ‒ December 2010) period at monthly intervals. The results showed that in only 20 instances out of 72, the intra-class correlation coefficients were greater than 0.5, but after bias correction, 64 instances out of 72 have intra-class correlations greater than 0.5. Therefore, the Mandel’s bundle of lines approach improves consensus among the experts by enforcing better statistical calibration. Published on 2018-03-28 05:29:02
       
  • C3 cubic trigonometric B-spline curves with a real parameter

    • Abstract: This paper presents a class of cubic trigonometric B-spline curves with a real parameter α, which are called α-B-spline curves. The α-B-spline curves have properties similar to those of the standard cubic uniform B-spline curves. In particular, the α-B-spline curves are C3 and can achieve shape adjustment by altering the value of the parameter α even if the control points are kept unchanged. With proper conditions, the α-B-spline curves also can exactly represent arcs of ellipses and parabolas. In order to obtain smooth α-B-spline curves, a method for determining the value of parameter α is presented. Published on 2018-03-28 05:26:51
       
  • Some topological indices of the family of nanostructures of polycyclic
           aromatic hydrocarbons (PAHs)

    • Abstract: Molecular descriptors play a significant role in many areas such as chemistry and pharmacology. Among these, topological indices have a prominent place. In this paper, we focus on the structure of polycyclic aromatic hydrocarbons and calculate theta, Pi and Sadhana indices of nanostructures. These indices on the ground of quasi-orthogonal cut ‘qoc’ edge strips in molecular graph. Also, the exact formulae for connectivity indices of nanotubes and nanotori are presented in this manuscript. These topological indices are useful for surveying structure of nanostructures, which have a relationship with degrees of their vertices. Published on 2018-03-28 05:24:27
       
  • Growth responses of Lantana (Lantana camara L.) varieties to varying water
           availability and light conditions

    • Abstract: Lantana camara L. (Verbenaceae) is an invasive alien species in many countries that causes economic losses and harmful ecological impacts on biodiversity. Its varieties with colourful flowers are being introduced to the horticulture trade in Sri Lanka despite that the orange-red flowered L. camara var. splendens and yellow-pink flowered L. camara var. camara introduced to the country in the nineteenth century have been naturalised and considered as invasive alien species of national significance. This study compared drought and shade tolerance abilities of white and purple flowered ornamental L. camara varieties with the above two naturalised varieties using statistical analysis. The results provided evidences for significant differences in drought and shade tolerance abilities between naturalised and ornamental L. camara varieties in Sri Lanka with regard to growth of the main stem, flowering, fruiting, defoliation, leaf water content and leaf growth rate, leaf area, photosynthetic tissue mass and pigment content, stomatal density, root volume and biomass partition between above and below ground parts. While contributing to fill in the knowledge gap in the biology of ‘Lantana group’, we report that ornamental L. camara varieties are not drought and shade tolerant as the naturalised varieties, and therefore their potential invasiveness may not be as high as the wild varieties that pose a great threat to the biodiversity of Sri Lanka. Published on 2018-03-28 05:22:00
       
  • Spatio-temporal variation of water quality and bio indicators of the
           Badulu Oya in Sri Lanka due to catchment disturbances

    • Abstract: Safe and ample supply of freshwater is fundamental to humans and for the sustainability of ecosystem function. Therefore, impacts of catchment disturbances on surface water quality have been given special attention currently. The Badulu Oya sub-catchment of the Upper Mahaweli catchment area in Sri Lanka is one of the landscapes affected by intensive agricultural activities and urban development. This study was aimed at evaluating the spatial and temporal variation of water quality, stream physical habitat quality and macroinvertebrate bioindicators in the Badulu Oya catchment area in relation to disturbances due to agricultural and urban practices. Physicochemical water quality parameters and macroinvertebrate indices were evaluated at ten sampling sites in the Badulu Oya catchment area within a one year period. The results revealed that water quality variables such as electrical conductivity (EC), total solids (TS), total dissolved solids (TDS), dissolved oxygen (DO), alkalinity, nitrate-N(NO3-N) and physical variables such as stream channel quality index (CQI) and riparian quality index (RQI) are significantly influenced by the degree of catchment disturbances. Among the macroinvertebrate indices tested, total abundance and family richness significantly varied with the degree of catchment disturbances. The findings of the present study revealed that the land use practices of Badulu Oya catchment result in significant impacts on stream ecological health. Similarly the study also revealed the prospect of using attributes such as water quality, physical habitat quality and macroinvertebrate bioindices for river health monitoring programmes. Published on 2018-03-28 05:18:01
       
  • A mathematical model with control to analyse the dynamics of dengue
           disease transmission in urban Colombo

    • Abstract: Dengue is a mosquito-borne disease. It has been an important public health problem particularly in the tropical and sub-tropical regions in the world, for which no vaccine or successful treatment has been found. Therefore, prevention and control play a vital role in minimising the risk of dengue in vulnerable populations.Various mathematical models such as the SIR model have been developed to understand the transmission dynamics of dengue. The main drawback of these dynamic models is the lack of predictability with respect to external factors such as climate, geography, demography and human behaviour due to usage of fixed parameters. The mosquito density, which depends heavily on various external factors such as climate is a critical parameter of these models and is responsible for the local transmission of the disease. In this study, the mosquito density is modelled with respect to changing levels of climate favourable for mosquito reproduction. A climate risk index developed using fuzzy set theory is used to vary the mosquito density with respect to rainfall and temperature and this measure is included in the SIR model.Finally, two measures, u1 and u2, are introduced to control adult mosquitoes and growing juveniles using two methods. The first method is theoretical where we consider u1 and u2 as random processes from uniform distribution. The second method involves continuous and constant control measures over time. The numerical results of the SIR model suggest that the dynamics of infections has changed and the number of infections is reduced as the efficiency of the control measures increase. Published on 2018-03-28 05:17:54
       
  • Collector cable design based on dynamic line rating for wind energy
           applications

    • Abstract: Wind power will play a major role in future power generation systems. In order to promote more and more wind farm connections, the capital cost (CAPEX) should be minimised. In this paper a novel concept is presented based on two practical considerations, namely, the actual current through different sections of a radially connected wind turbine string reduces from the substation end to the farthest wind turbine; and the current carrying capacity of a conductor and wind turbine current increases with the wind speed. Two tools that support the design of the collector network and ensure safe operation of the overhead collector conductors were developed. The first tool aids the designing of the collector conductors based on the dynamic line rating of the conductor and the actual wind farm output at different wind speeds. The second tool is a verification tool, which ensures that the conductor core temperature does not exceed the maximum allowable conductor temperature. A case study is presented to demonstrate the use of the design tool whereas a real life implementation is used to demonstrate that the verification tool can be used in a real wind farm to ensure the safety of the conductors. Published on 2018-03-28 04:58:18
       
  • Genetic analysis of yield and physical traits of spring wheat grain

    • Abstract: The economic value of wheat grain is determined by morphology, texture and size of grain. Very little knowledge is available about the genetic inheritance pattern of the physical characteristics of wheat grain. The mechanical properties of wheat kernel have direct or indirect link on the milling and baking quality of wheat. Six bread wheat genotypes/lines were crossed in all possible combinations in order to assess the genetic inheritance pattern and combining ability of the grain’s physical properties. Additive type of gene action was involved in number of spikelets per spike, spike length, number of grains per spike, grain weight and grain area. Therefore, selection of superior plants can be done in early generations for development of better wheat genotypes. Grain yield per spike, grain width, grain length, grain height and grain sphericity having nonadditive type of gene actions clearly indicated that selection of superior plants should be postponed to later generations. The genotype 9481 was the best general combiner, while among the crosses 1 × 3 and 4 × 6 exhibited the highest positive specific combining ability in most of the prominent traits. This study will be useful for wheat breeders to develop high yielding genotypes with better grain architecture to improve the milling and baking quality of bread wheat. Published on 2018-03-28 04:57:44
       
 
 
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