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Search Results: 1 - 10 of 560 matches for " Laurie CUTHBERT "
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QoS in Node-Disjoint Routing for Ad Hoc Networks  [PDF]
Luo LIU, Laurie CUTHBERT
Int'l J. of Communications, Network and System Sciences (IJCNS) , 2008, DOI: 10.4236/ijcns.2008.11011
Abstract: Ad hoc network (MANET) is a collection of mobile nodes that can communicate with each other without using any fixed infrastructure. To support multimedia applications such as video and voice MANETs require an efficient routing protocol and quality of service (QoS) mechanism. Node-Disjoint Multipath Routing Protocol (NDMR) is a practical protocol in MANETs: it reduces routing overhead dramatically and achieves multiple node-disjoint routing paths. QoS support in MANETs is an important issue as best-effort routing is not efficient for supporting multimedia applications. This paper presents a novel adaptation of NDMR, QoS enabled NDMR, which introduces agent-based SLA management. This enhancement allows for the intelligent selection of node-disjoint routes based on network conditions, thus fulfilling the QoS requirements of Service Level Agreements (SLAs).
Erlang's Fixed-Point Approximation for Performance Analysis of HetNets
Guozhi Song,Jigang Wu,John Schormans,Laurie Cuthbert
Journal of Applied Mathematics , 2012, DOI: 10.1155/2012/862809
Abstract: We consider the analytic modelling of wireless systems with multiple access technologies in the perspective of teletraffic engineering and provide a framework for the performance analysis and evaluation of a wireless HetNet (heterogeneous network) system with both cellular and WLAN access technologies. In particular, an approach with Erlang's fixed-point approximation to calculate the new call blocking and handover call dropping probabilities in such systems is introduced. The model is versatile enough to cover not only cellular/WLAN HetNet systems but other wireless HetNets with difference access technologies in general.
Vector perturbation based adaptive distributed precoding scheme with limited feedback for CoMP systems
Zhang Tiankui,Shen Xiaochen,Cuthbert Laurie,Xiao Lin
EURASIP Journal on Wireless Communications and Networking , 2011,
Abstract: A downlink adaptive distributed precoding scheme is proposed for coordinated multi-point (CoMP) transmission systems. The serving base station (BS) obtains the optimal precoding vector via user feedback. Meanwhile, the precoding vector of each coordinated BS is determined by adaptive gradient iteration according to the perturbation vector and the adjustment factor based on the vector perturbation method. In each transmission frame, the CoMP user feeds the precoding matrix index back to the serving BS, and feeds back the adjustment factor index to the coordinated BSs, which can reduce the uplink feedback overhead. The selected adjustment factor for each coordinated BS is obtained via the precoding vector of the coordinated BS used in the previous frame and the preferred precoding vector of the serving BS in this frame. The proposed scheme takes advantage of the spatial non-correlation and temporal correlation of the distributed MIMO channel. The design of the adjustment factor set is given and the channel feedback delay is considered. The system performance of the proposed scheme is verified with and without feedback delay respectively and the system feedback overhead is analyzed. Simulation results show that the proposed scheme has a good trade-off between system performance and the system control information overhead on feedback.
Mutual Coupling Effects on Pattern Diversity Antennas for MIMO Femtocells
Yue Gao,Shihua Wang,Oluyemi Falade,Xiadong Chen,Clive Parini,Laurie Cuthbert
International Journal of Antennas and Propagation , 2010, DOI: 10.1155/2010/756848
Abstract: Diversity antennas play an important role in wireless communications. However, mutual coupling between multiple ports of a diversity antenna has significant effects on wireless radio links and channel capacity. In this paper, dual-port pattern diversity antennas for femtocell applications are proposed to cover GSM1800, UMTS, and WLAN frequency bands. The channel capacities of the proposed antennas and two ideal dipoles with different mutual coupling levels are investigated in an indoor environment. The relation between mutual coupling and channel capacity is observed through investigations of these antennas. 1. Introduction Driven by demands from mobile users, there is nowadays a strong requirement to provide sustainable data rates everywhere, not just reception of signals. According to recent surveys, 50% of mobile phone calls and 70% of mobile data services will take place indoors in the next few years [1]. Using macrocells to provide coverage is expensive when serving indoor customers who require high data rates and QoS (Quality of Service). FAPs (Femtocell access points) or home-base stations [2] have been proposed in such a scenario to enhance the coverage and data rate. An FAP is a low-power access point that is built using a standard air interface (GSM, UMTS, or LTE), while the backhaul connection makes use of a broadband connection such as optical fibre or DSL (Digital Subscriber Line). The use of femtocells benefits both users and operators. Users enjoy a better signal quality due to the proximity between transmitter and receiver. Since indoor traffic is transmitted over the IP backhaul, femtocells help the operator to manage the exponential growth of traffic and increase the reliability of macrocell networks. It has been shown from previous studies that a two-tier underlay with 50 femtocells per cell-site network can obtain a nearly 25 times improvement in overall spatial reuse compared to a macrocell-only network [2]. However, the cochannel deployment of such a large femtocell layer will impact existing macrocell networks, affecting their capacity and performance [3]. Femtocell in cochannel operation with an existing macrocellular network is technically more challenging, but is also more rewarding for the operator because of the potentially increased spectral efficiency per area through spatial frequency re-use. Especially in two-tier networks with universal frequency reuse, the near-far effect from cross-tier interference creates dead spots where reliable coverage cannot be guaranteed to users in either tier. Theoretical studies have shown
Bicarbonate Secretion in the Murine Gallbladder - Lessons for the Treatment of Cystic Fibrosis
Cuthbert AW
JOP Journal of the Pancreas , 2001,
Abstract: The epithelium lining the gallbladder of mammalian species has absorptive and secretory functions. An important function is the secretion of a bicarbonate rich fluid that helps neutralise stomach acid and provides an appropriate environment for intestinal enzymes. In cystic fibrosis (CF) this secretory function is lost. This study concerns the bicarbonate secreting activity of murine gallbladders in vitro using wild type and CF mice and four main questions are considered as follows: a) Does the murine gallbladder secrete bicarbonate electrogenically and is this prevented in CF? b) Can the secretory activity in CF gallbladders be restored by gene therapy or pharmacologically? c) How is the cystic fibrosis transmembrane conductance regulator (CFTR) involved in bicarbonate secretion? d) Does the data offer prospects for the treatment of CF?. Work from both the author's laboratory and the literature will be reviewed. Consideration of the currently available data indicates that the wild type murine gallbladder does secrete bicarbonate electrogenically and that this is absent in CF mice. Further it has been demonstrated that bicarbonate secretory activity can be restored by both gene therapy and by the use of drugs. The role of CFTR in bicarbonate secretion remains equivocal. Much evidence suggests that CFTR can act as a channel for HCO(3)(-) ions as well as Cl(-) ions, while others propose a parallel arrangement of CFTR with a Cl(-)/HCO(3)(-) exchanger is necessary. The matter is further complicated by the regulatory role of CFTR on other transporting activities. Opportunities for possible application to man are discussed.
Climate Change Adaptation and Vulnerability: A Case of Rain Dependent Small-Holder Farmers in Selected Districts in Zambia  [PDF]
Cuthbert Casey Makondo, Kenneth Chola, Blesswell Moonga
American Journal of Climate Change (AJCC) , 2014, DOI: 10.4236/ajcc.2014.34034
Abstract: Food crop production by small-holder farmers in Africa is particularly vulnerable to climate change, given high dependence on rainfall coupled with limited adaptive capacity. In Zambia, smallholder farmers contribute about 79% of national stable food requirements particularly maize. This paper attempted to establish levels of food security in each of the three agro-ecological zones of Zambia, and evaluated the current adaptive measures of rain dependent small-holder farmers against climate change risks. The challenges farmers are facing in adapting to the change risks were identified and livelihood vulnerability assessed. The findings indicate that rain dependent small-holder farmers in Zambia are highly vulnerable to weather related shocks which impact greatly on their food production; and that the levels of vulnerability vary across gender and per agro-ecological zone. After the evaluation of scenarios including staple food crop yields (maize), the authors conclude that most rain-fed small-holder farmers in Zambia (about 70%) are facing considerable hardships in adapting to the changing climate, which in turn, undermines their contribution to food security. While efforts by government have been made to assist farmers towards climate change adaptation, there still remains many challenges to achieve the desired outcomes. Most farmers (66%) are unable to afford certain alternatives, such as those of agro-forestry or conservation. Difficulties in accessing markets, poor road infrastructure, fluctuating market prices, high costs and late deliveries of farming in-puts were found to be among the major challenges that farmers are facing in Zambia. There are also no systematic early warning systems in place against natural hazards and disasters. This makes farming a difficult undertaking in Zambia.
Reciprocal Teaching of Lecture Comprehension Skills in College Students
Norman Spivey,Andrea Cuthbert
The Journal of Scholarship of Teaching and Learning , 2006,
Abstract:
Analysis of Energy Characteristics of Rice and Coffee Husks Blends
Cuthbert F. Mhilu
ISRN Chemical Engineering , 2014, DOI: 10.1155/2014/196103
Abstract: Production of first generation biofuels using food crops is under criticism over sustainability issues on food security. Tanzania is showing active interest in developing second generation biofuels to deal with some of such issues, especially from the feedstock point of view. This paper reports work done to determine energy characteristics of rice and coffee husks. The results show that coffee husks have better energy quality than rice husks, while heating values of coffee are 18.34?MJ/kg and 13.24?MJ/kg for rice husk. Thermogravimetric analysis made for coffee husks blended rice husks at a ratio of 75?:?25% vol. show better material degradation characteristics yielding low residual mass of 23.65%, compared to 26.50% of char and ash remaining in pure rice husks. Derivative thermogravimetric analysis shows comparable hemicellulose degradation peak values of ?11.5 and ?11.2 and cellulose ?3.20 and ?2.90 in pure coffee and rice husks, respectively. In coffee and rice husks blends, substantial reductions of hemicellulose and cellulose peaks were observed. Use of coffee and rice husks blends applying high temperature gasification would reduce the latter’s flammability, while increasing its flame retention characteristics, hence offering opportunities for production of clean syngas in a sustainable manner. 1. Introduction 1.1. Background and Goal For many years, we have consumed fossil fuels with no worries about possible shortages, but, now, those same oil fields are running dry, while use of coal as a source of energy is also facing criticisms due to its contribution on environmental pollution. In view of this situation, there has been a growing impetus looking for alternative sources of energy for the future. Biomass based second generation biofuels could partly assist to resolve some of these issues, especially from the feedstock point of view for energy production applying various conversion methods to improve the combustion efficiency. The advantages of using biomass are obvious as this material, is generally left to rot or burnt in an uncontrolled manner, producing CO2 as well as smoke. Most African countries are facing problems of inadequate access to modern sources of energy. The United Republic of Tanzania being one of the sub-Saharan African countries is showing active interest in the development of the second generation biofuels, especially from the feedstock point of view to address criticism over sustainability issues as well as arguments on food security arising from the production of 1st generation biofuels derived from food crops materials to
Modelling the Suitability of Pine Sawdust for Energy Production via Biomass Steam Explosion  [PDF]
Zephania Chaula, Mahir Said, Geoffrey John, Samwel Manyele, Cuthbert Mhilu
Smart Grid and Renewable Energy (SGRE) , 2014, DOI: 10.4236/sgre.2014.51001
Abstract:

Biomass material as a source of fuel is difficult to handle, transport, store, and utilize in its original form. To overcome these challenges and make it suitable for energy prodution, the material must be pre-treated. Biomass steam explosion is one of the promising pretreatment methods where moisture and hemicellulose are removed in order to improve biomass storage and fuel properties. This paper is aimed to model the suitability of pine saw dust for energy production through steam explosion process. The peak property method was used to determine the kinetic parameters. The model has shown that suitable operating conditions for steam explosion process to remove moisture and hemicellulose from pine sawdust. The temperature and pressure ranges attained in the current study are 260 -317 (533 -590 K), 4.7 -10.8 MPa, respectively.

Addressing Challenges in the Management of Paediatric Intussusceptions in the District Hospital  [PDF]
Senyo Gudugbe, Jonathan Cuthbert Balea Dakubo, Samuel Essoun
Open Journal of Pediatrics (OJPed) , 2014, DOI: 10.4236/ojped.2014.44035
Abstract: Intussusception is the leading cause of intestinal obstruction in children and its management can be challenging especially in centres with inadequate resources where this problem becomes more daunting. Nineteen cases of intussusception in the paediatric age group which were managed by medical officers in a district Hospital in Ghana are discussed. The outcomes of cases treated by open surgery, and those managed by pneumatic reduction were studied. We highlight the use of an improvised set up used in achieving pneumatic reduction thereby obviating operative reduction.
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