Science
http://repository.kln.ac.lk/handle/123456789/1
2017-09-23T10:08:03ZMulti-mesh gillnet selectivity of Oreochromis mossambicus and O. niloticus (Cichlidae) in the fishery of three large perennial reservoirs in Sri Lanka
http://repository.kln.ac.lk/handle/123456789/17245
Multi-mesh gillnet selectivity of Oreochromis mossambicus and O. niloticus (Cichlidae) in the fishery of three large perennial reservoirs in Sri Lanka
Jayasinghe, R.P.P.K.; Amarasinghe, U.S.; Moreau, J.
As in many tropical reservoir fisheries, the major fishing gear in the reservoirs of Sri Lanka is gillnet. Gillnets of a wide range of stretched mesh sizes (6.9 - 11.4 cm) are used in individual boats in Sri Lankan reservoirs targeting mainly two exotic cichlid species, Oreochromis mossambicus and O. niloticus, which dominate the fisheries accounting for over 80% of the landings. Although the filament characteristics and dimensions of gillnets of different mesh sizes are uniform, their mesh composition varies from boat to boat making catch samples in individual boats are under the influence of different selectivity patterns. As such, an approach is presented for constructing the overall selection curves in the sampled boats during different sampling occasions for the two cichlid fish species in the three reservoirs. For this purpose, gillnet selectivity of each mesh size was determined using Baranov-Holt method. Probabilities of capture of mesh-wise gillnet selection curves were then summed up giving weight to the contribution of each mesh size to the total number of net pieces in the sampled boat, to determine the overall gillnet selection from gillnets of all mesh sizes. The importance of the findings of the present study for length-based stock assessment methods and for imposing mesh regulations to the gillnet fisheries in reservoirs of Sri Lanka is discussed.
2017-01-01T00:00:00ZA comparative analysis on the effects of river discharge on trophic interactions in two tropical streams.
http://repository.kln.ac.lk/handle/123456789/17244
A comparative analysis on the effects of river discharge on trophic interactions in two tropical streams.
Weliange, W.S.; Amarasinghe, U.S.; Vijverberg, J.; Leichtfried, M.; Füreder, L .
Discharge-mediated seasonal patterns of food web interactions were investigated in two streams in Sri Lanka; Eswathu Oya (a perennial wet-zone stream) and Yan Oya (a seasonal dry-zone stream). Based on volumetric proportions of diet composition, relative abundance of fish species and their daily food rations, the mean cumulative consumption of each prey taxon was estimated for each fish population. Food web diagrams were prepared using trophic index of fish, trophic class of prey and feeding interactions between fish and prey. Both streams showed seasonal patterns of discharge due to rainfall, but no significant effect was evident in the trophic index of most fish species. In both streams, cumulative consumption of prey taxa was highest during low discharge regime due to increased abundance of both prey taxa and consumers. In Eswathu Oya, diversity of prey taxa was higher during the low discharge regime, but in Yan Oya, high diversity occurred during the high discharge regime. Herbivorous and/or detritivorous fish species were rare in Eswathu Oya but dominant in Yan Oya. Complex food web structure in Yan Oya due to high fish species richness and high diversity of prey categories made it less sensitive to discharge extremes in contrast to relatively simple food web structure in Eswathu Oya. This study, therefore, highlights the importance of maintaining the quality of riparian environments for conservation of biodiversity.
2017-01-01T00:00:00ZAnalysis of a stochastic predator-prey model
http://repository.kln.ac.lk/handle/123456789/207
Analysis of a stochastic predator-prey model
Prasadini, K.D.S.; Mallawa Arachchi, D.K.
In biological systems Lotka-Volterra predator-prey model describes the population
dynamics of two interacting species of predators and its preys. Classical predatorprey
model is a primitive deterministic model governed by the two differential
equations, namely,
���� = (������ − ��������) ���� and ���� = (�������� − ������) ����
where �� and �� denote prey and predator respectively, and ����, ����, ���� and ���� are
parameters.
This model can be improved by introducing stochasticity that accounts for the
random fluctuations of a realistic predator-prey dynamical system. In this research
work, we use Stochastic Differential Equation (SDE) approach. There are various
ways, based on various assumptions, to incorporate SDE. One common approach is
to use equations of the following form:
���� = (������ − ��������) ���� + ��(���� + ����)�� ������
���� = (�������� − ������) ���� + ��(���� + ����)�� ������
These types of Stochastic Differential Equations (SDE) can be simulated in Matlab
using numerical methods such as Euler-Maruyama method. Phase planes of the
deterministic and stochastic models are carried out to demonstrate the behavior of
this modified model.
Our initial goal is to compare different stochastic models with the original
deterministic model through simulations. The deterministic model has a positive
equilibrium which is globally stable for positive values of the parameters.
Nevertheless, in the stochastic model, the predator and prey populations may tend to
extinction. Extinction percentages of predator or prey population are summarized
and analyzed through this research work.
2016-01-01T00:00:00ZThe chromatic number of prime graph of a noncommutative ring Mn×n(Z2)
http://repository.kln.ac.lk/handle/123456789/206
The chromatic number of prime graph of a noncommutative ring Mn×n(Z2)
Kolombage, K.A.D.D.B.V.; Wijesiri, G.S.
Graph theory is a significant area of Mathematics as its outstanding applications in
many fields such as biochemistry, electrical engineering, computer science and
operational research. Besides Graph theory, Ring theory is an abstract area in
Mathematics. A ring consists of a set equipped with two binary operations that
generalize the arithmetic operations of addition (+) and multiplication(∗). Theorems
obtained as a result of abstract study of rings can be applied to solve problems arising
in number theory, geometry and many other fields.
The study of rings with the help of graphs began when a graph of a commutative ring
was defined by I. Beck in 1988. Then a new bridge was formed between graph theory
and the algebraic concept “ring” noted as prime graph of a ring ��, denoted by ����(��)
by B. Satyanarayana, K. Shyam Prasad, and D.Nagaraju in 2010. Later on with the
help of existing concepts, K. Patra and S. Kalita investigated the chromatic number
of prime graph, ������(ℤ��) of ring ℤ�� for different values of ��.
Prime graph of a ring �� is a graph whose vertices are all elements of the ring and any
two vertices ��, �� of the vertex set are adjacent if and only if �� ∗ �� = 0 or �� ∗ �� = 0
and �� ≠ ��
In this paper, we investigate the chromatic number of prime graph of some noncommutative
rings ����×��(ℤ��) for different values of n. The chromatic number of
prime graph of some commutative rings are formed on the recognition of the
conjecture that chromatic number, ��(��) and clique number are the same. But for
non-commutative rings this is not always the case. Hence, in order to find the
chromatic number of prime graph of a non-commutative ring, ����×��(ℤ��), we have
looked into MATLAB for a tactical solution.
2016-01-01T00:00:00Z