OALib Journal期刊

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匹配条件: “T. G. Tharaka Kusuminda” ,找到相关结果约283836条。
Re-discovery of Pouch bearing sheath tailed bat Saccolaimus saccolaimus Temminck (Chiroptera: Emballonuridae) from Sri Lanka after 75 years
Ranil P. Nanayakkara,Nilantha Vishvanath,T. G. Tharaka Kusuminda
Asian Journal of Conservation Biology , 2012,
Abstract: Saccolaimus saccolaimus Temminck, 1838, was first collected by the Museum of Natural History of Sri Lanka in the year 1919 and the first published record of this bat was in 1935 by W.W.A. Philips, though specimens were collected at various times for the collection of the Natural History Museum of Sri Lanka. However, after 1936 there were no records of the species, though, several surveys were conducted on the bat fauna of the island. The species had not been reported since, and was considered as Data Deficient according to latest literature. Here we report on its re-discovery.
The Range Extension of the Critically Endangered, Poecilotheria smithi in Sri Lanka, with Notes on its Sociality
Ranil P. Nanayakkara,Nilantha Vishvanath,T. G. Tharaka Kusuminda,G.A.S.M. Ganehiarachchi
Asian Journal of Conservation Biology , 2013,
Abstract: Poecilotheria smithi is a Critically Endangered Theraposid known only from the type locality Haragama in the Kandy District, Sri Lanka. It was thought to be distribution specific to Haragama. During a survey on the genus Poecilotheria, which was initiated in 2011 by the authors, P. smithi was recorded, the first confirmed observation of P. smithi outside of its type locality from the Matale district about 31.42 Km in aerial distance northwest of the type locality. Distribution of this species extended in Sri Lanka by this novel record. P. smithi displays the social behaviour of sharing same microhabitat with few individuals. As demonstrated for P. smithi, we suggest the large group size and social behaviour observed was in response to unavailability of suitable micro habitat for the mature individuals.
Vector Broadcast Channels: Optimal Threshold Selection Problem
Tharaka Samarasinghe,Hazer Inaltekin,Jamie Evans
Mathematics , 2011,
Abstract: Threshold feedback policies are well known and provably rate-wise optimal selective feedback techniques for communication systems requiring partial channel state information (CSI). However, optimal selection of thresholds at mobile users to maximize information theoretic data rates subject to feedback constraints is an open problem. In this paper, we focus on the optimal threshold selection problem, and provide a solution for this problem for finite feedback systems. Rather surprisingly, we show that using the same threshold values at all mobile users is not always a rate-wise optimal feedback strategy, even for a system with identical users experiencing statistically the same channel conditions. By utilizing the theory of majorization, we identify an underlying Schur-concave structure in the rate function and obtain sufficient conditions for a homogenous threshold feedback policy to be optimal. Our results hold for most fading channel models, and we illustrate an application of our results to familiar Rayleigh fading channels.
Vector Broadcast Channels: Optimality of Threshold Feedback Policies
Tharaka Samarasinghe,Hazer Inaltekin,Jamie Evans
Mathematics , 2011,
Abstract: Beamforming techniques utilizing only partial channel state information (CSI) has gained popularity over other communication strategies requiring perfect CSI thanks to their lower feedback requirements. The amount of feedback in beamforming based communication systems can be further reduced through selective feedback techniques in which only the users with channels good enough are allowed to feed back by means of a decentralized feedback policy. In this paper, we prove that thresholding at the receiver is the rate-wise optimal decentralized feedback policy for feedback limited systems with prescribed feedback constraints. This result is highly adaptable due to its distribution independent nature, provides an analytical justification for the use of threshold feedback policies in practical systems, and reinforces previous work analyzing threshold feedback policies as a selective feedback technique without proving its optimality. It is robust to selfish unilateral deviations. Finally, it reduces the search for rate-wise optimal feedback policies subject to feedback constraints from function spaces to a finite dimensional Euclidean space.
Optimal Selective Feedback Policies for Opportunistic Beamforming
Tharaka Samarasinghe,Hazer Inaltekin,Jamie S. Evans
Mathematics , 2011,
Abstract: This paper studies the structure of downlink sum-rate maximizing selective decentralized feedback policies for opportunistic beamforming under finite feedback constraints on the average number of mobile users feeding back. Firstly, it is shown that any sum-rate maximizing selective decentralized feedback policy must be a threshold feedback policy. This result holds for all fading channel models with continuous distribution functions. Secondly, the resulting optimum threshold selection problem is analyzed in detail. This is a non-convex optimization problem over finite dimensional Euclidean spaces. By utilizing the theory of majorization, an underlying Schur-concave structure in the sum-rate function is identified, and the sufficient conditions for the optimality of homogenous threshold feedback policies are obtained. Applications of these results are illustrated for well known fading channel models such as Rayleigh, Nakagami and Rician fading channels, along with various engineering and design insights. Rather surprisingly, it is shown that using the same threshold value at all mobile users is not always a rate-wise optimal feedback strategy, even for a network with identical mobile users experiencing statistically the same channel conditions. For the Rayleigh fading channel model, on the other hand, homogenous threshold feedback policies are proven to be rate-wise optimal if multiple orthonormal data carrying beams are used to communicate with multiple mobile users simultaneously.
Transmission Rank Selection for Opportunistic Beamforming with Quality of Service Constraints
Meng Wang,Tharaka Samarasinghe,Jamie Evans
Mathematics , 2014,
Abstract: In this paper, we consider a multi-cell multi-user MISO broadcast channel. The system operates according to the opportunistic beamforming framework in a multi-cell environment with variable number of transmit beams (may alternatively be referred as the transmission rank) at each base station. The maximum number of co-scheduled users in a cell is equal to its transmission rank, thus increasing it will have the effect of increasing the multiplexing gain. However, this will simultaneously increase the amount of interference in the network, which will decrease the rate of communication. This paper focuses on optimally setting the transmission rank at each base station such that a set of Quality of Service (QoS) constraints, that will ensure a guaranteed minimum rate per beam at each base station, is not violated. Expressions representing the achievable region of transmission ranks are obtained considering different network settings. The achievable transmission rank region consists of all achievable transmission rank tuples that satisfy the QoS constraints. Numerical results are also presented to provide further insights on the feasibility problem.
Optimizing user selection schemes in vector broadcast channels
Meng Wang,Tharaka Samarasinghe,Jamie S. Evans
Mathematics , 2014,
Abstract: In this paper, we focus on the ergodic downlink sum-rate performance of a system consisting of a set of heterogeneous users. We study three user selection schemes to group near-orthogonal users for simultaneous transmission. The first scheme is a random selection policy that achieves fairness, but does not exploit multi-user diversity. The second scheme is a greedy selection policy that fully exploits multi-user diversity, but does not achieve fairness, and the third scheme achieves fairness while partially exploiting multi-user diversity. We also consider two beamforming methods for data transmission, namely, maximum-ratio transmission and zero-forcing beamforming. In all scheduling schemes studied in the paper, there is a key parameter that controls the degrees of orthogonality of channel directions between co-scheduled users. We focus on optimally setting this parameter for each scheduling scheme such that the ergodic downlink sum-rate is maximized. To this end, we derive analytical expressions for the ergodic downlink sum-rate considering each scheduling scheme. Numerical results are also presented to provide further insights.
Outage Capacity of Opportunistic Beamforming with Random User Locations
Tharaka Samarasinghe,Hazer Inaltekin,Jamie Evans
Computer Science , 2013,
Abstract: This paper studies the outage capacity of a network consisting of a multitude of heterogenous mobile users, and operating according to the classical opportunistic beamforming framework. The base station is located at the center of the cell, which is modeled as a disk of finite radius. The random user locations are modeled using a homogenous spatial Poisson point process. The received signals are impaired by both fading and location dependent path loss. For this system, we first derive an expression for the beam outage probability. This expression holds for all path loss models that satisfy some mild conditions. Then, we focus on two specific path loss models (i.e., an unbounded model and a more realistic bounded one) to illustrate the applications of our results. In the large system limit where the cell radius tends to infinity, the beam outage capacity and its scaling behavior are derived for the selected specific path loss models. It is shown that the beam outage capacity scales logarithmically for the unbounded model. On the other hand, this scaling behavior becomes double logarithmic for the bounded model. Intuitive explanations are provided as to why we observe different scaling behavior for different path loss models. Numerical evaluations are performed to give further insights, and to illustrate the applicability of the outage capacity results even to a cell having a small finite radius.
Toxoplasma, Toxocara and Tuberculosis co-infection in a four year old child
Randeewari Guneratne, Devan Mendis, Tharaka Bandara, Sumadhya Fernando
BMC Pediatrics , 2011, DOI: 10.1186/1471-2431-11-44
Abstract: This case report describes a co-infection of Toxoplasma gondii, Toxocara spp and tuberculosis in a child with chronic lymphadenopathy and eosinophilia.The case report highlights two important points. First is the diagnostic challenges that are encountered by clinicians in tropical countries such as Sri Lanka, where lymphadenopathy and eosinophilia with a positive serology commonly point towards a parasitic infection. Secondly the importance of proper history taking and performing the Mantoux test as a first line investigation in a country where the incidence of tuberculosis is low, even in the absence of a positive contact history.Tuberculosis. toxocariasis and toxoplasmosis are among the common infectious causes of lymphadenitis in children [1]. Approximately 250,000 children worldwide develop tuberculosis, a larger proportion being reported from the South East Asian region [2,3]. Extra-pulmonary tuberculosis is more common in children, the most common form being lymphatic disease accounting for about two thirds of the cases of extra-pulmonary tuberculosis [4-6].Toxoplasma gondii and Toxocara spp. infections are cosmopolitan zoonotic diseases which may cause systemic and ocular diseases in humans [7-9]. Few publications exist regarding Toxoplasma and Toxocara co-infection [10,11].This case report describes a child with chronic lymphadenopathy and eosinophilia who was seropositive for both Toxoplasma gondii and Toxocara spp, together with a positive Mantoux test and lymph node histology suggesting tuberculosis.A 4 year-old, previously healthy boy was admitted to the surgical unit of the Colombo South Teaching Hospital, Sri Lanka with an abscess in the left big toe. No fever or local lymphadenopathy was present at initial presentation. The abscess was drained, treated with antibiotics and the child was discharged. Two weeks later the child was re-admitted with an infection at the site of original abscess and left sided inguinal lymphadenopathy. Full blood count (FBC)
Problem-Elephant Translocation: Translocating the Problem and the Elephant?
Prithiviraj Fernando, Peter Leimgruber, Tharaka Prasad, Jennifer Pastorini
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0050917
Abstract: Human-elephant conflict (HEC) threatens the survival of endangered Asian elephants (Elephas maximus). Translocating “problem-elephants” is an important HEC mitigation and elephant conservation strategy across elephant range, with hundreds translocated annually. In the first comprehensive assessment of elephant translocation, we monitored 16 translocations in Sri Lanka with GPS collars. All translocated elephants were released into national parks. Two were killed within the parks where they were released, while all the others left those parks. Translocated elephants showed variable responses: “homers” returned to the capture site, “wanderers” ranged widely, and “settlers” established home ranges in new areas soon after release. Translocation caused wider propagation and intensification of HEC, and increased elephant mortality. We conclude that translocation defeats both HEC mitigation and elephant conservation goals.

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