Effect of 3 Key Factors on Average End to End Delay and Jitter in MANET

A mobile ad-hoc network (MANET) is a self-configuring infrastructure-less network of mobile devices connected by wireless links where each node or mobile device is independent to move in any desired direction and thus the links keep moving from one node to another. In such a network, the mobile nodes are equipped with CSMA/CA (carrier sense multiple access with collision avoidance) transceivers and communicate with each other via radio. In MANETs, routing is considered one of the most difficult and challenging tasks. Because of this, most studies on MANETs have focused on comparing protocols under varying network conditions. But to the best of our knowledge no one has studied the effect of other factors on network performance indicators like throughput, jitter and so on, revealing how much influence a particular factor or group of factors has on each network performance indicator. Thus, in this study the effects of three key factors, i.e. routing protocol, packet size and DSSS rate, were evaluated on key network performance metrics, i.e. average delay and average jitter, as these parameters are crucial for network performance and directly affect the buffering requirements for all video devices and downstream networks

The Spetzler-Martin grading system and management of patients with intracranial Arteriovenous malformation in a tertiary referral hospital

Introduction: An arteriovenous malformation (AVM) is an abnormal collection of blood vessels in which arterial blood flows directly into the draining vein without the normal interposed capillaries. The Spetzler-Martin grading system has been widely accepted worldwide to estimate the pretreatment risks and predict the outcome of patients with intracranial AVM. In Malaysia, we still do not have the baseline data of this grading system. Methods: A total of 33 patients from a tertiary referral hospital diagnosed with intracranial AVM based on neuroimaging findings over a 4-year period were studied. Medical records were traced and neuroimaging findings were analysed. The AVMs were graded according to the Spetzler-Martin grading system and Fisher’s exact test was used to assess statistical difference between the grades of the AVM and management plan for the patients. Results: Four patients were graded as Grade 1, 9 patients as Grade II, 10 patients as Grade III, 6 patients as Grade IV and 4 patients as Grade V. Ten patients were treated conservatively; six patients underwent surgery and embolisation respectively. Four patients underwent radiosurgery and a combination of embolisation while surgery and radiosurgery were given to 5 patients and 2 patients respectively. Statistically significant difference (p=0.016) was found between the Spetzler-Martin grading system and the management of intracranial AVMs. Conclusion: The management decision was not made based on the grading of the AVMs. It is recommended that all AVM patients be routinely graded according to this system prior to treatment. Keywords: Intracranial arteriovenous malformation

Performance evaluation of seed values and pause times over high speed Wireless Campus Network in IEEE802.11e

IEEE802.11e standard assures to provide QoS using service differentiation mechanism over WLAN. The Enhanced Distributed Channel Access (EDCA) mechanism employs to differentiate the multimedia traffic based on assigned priorities and allows accessing the channel.Only one category of traffic permits access to the channel at a time to avoid traffic collision over the network. In EDCA, the back-off window algorithm generates back-off window size randomly during traffic transmission through the channel to prevent other categories of traffic to access the channel. Due to this randomness of back-off window algorithm to provide probabilistic QoS to satisfy the multimedia traffic through the network, the random mobility model can reduce the network performance. In this paper, we analyze the proposed network performance based on the variation of randomness using different seed values according to different pause time and evaluate the network performance using various performance metrics in IEEE802.11e

The impact of randomness on high speed wireless campus network in IEEE802.11e

The enhancement of channel access mechanism assures to provide Quality of Service (QoS) using the service differentiation mechanism over WLAN in IEEE802.11e. The service differentiation scheme is used in the Enhanced Distributed Channel Access (EDCA) MAC layer protocol and this protocol is used the random back-off window algorithm to provide QoS for the real time multimedia applications. However, the back-off window mechanism ensures QoS to satisfy multimedia traffic but it only the probabilistic QoS due to the random nature of the algorithm. As like as the randomness of the mobility models that can be reduced the network performance. In this paper, we analyze the proposed network performance based on the variation of randomness using different seed values and evaluate the network performance using various performance metrics in IEEE802.11e

Verification of weibull's theory of brittle fracture for local timber loaded in tension parallel to grain

Conventional brittle fracture theory (or statistical strength theory) has been developed on the basis of the weakest link concept proposed by Pierce, who studied cotton yarns, and Tucker, who studied concrete [1]. Major developments of the theory were made by Weibull [2], who verified his results with tests on many different brittle materials, but apparently not timber. Weibull showed how the strength of a weakest link system can be explained by a cumulative distribution of the exponential type, and how the strength depends on the volume of the test specimen for uniform or varying distributions of stress within the specimen. The first study in which the Weibull brittle fracture theory was applied to timber was reported by Bohannan [3]. He studied clear timber beams and found that for geometrically similar beams the strength was proportional to the depth of the beam to the power 1/9, this being the result of a depth effect and a length effect of equal importance. He found that strength was not affected by beam breadth

Verification of weibull's theory of brittle fracture to meranti's timber loaded in tension parallel to the grain

Timber is a well-known brittle material under tensile load and is also an inhomogeneous material. Although Weibull's theory of brittle fracture is well established for softwood timber, the verification of this theory to hardwood species, particularly to the timber of local species is very limited. This paper presents the verification of Weibull’s theory to local timber of Meranti species loaded in tension parallel to the grain. The theoretical prediction is compared to the test results. It is found that the variation of tensile strength at several probabilities is in close agreement with theoretical prediction. Two values of Weibull's parameters were proposed in the formulation to predict the tensile strength for local timber. It is also found that the tensile strength of local timber is affected by its volume

An improved strain incremental formulation in boundary element method applied to a timber beam at the moment of failure

A major formulating problem in boundary element method applied to plasticity problem is a singularity of strain incremental formulation at plastic region. This singularity arises from the singularity of Kernel stress derivative and it is a second order singularity. Brebbia, et al. [1] presents a method to solve the second order singularity problem by expanding the singular integral to reduce to non-singular integral. This method is supported by Kane [2]. Telles and Brebbia [3] also proposed indirect method to solve hypersingular integral. By using transformation method, and combine with Guiggiani and Gigante work [4], Leitao [5] extended Brebbia, et al. works to solve the second order singularity problem. The previous methods to solve the second order singularity problem require further improvement. This paper proposed a new and improved technique to solve this type of problem

Ultimate load prediction for timber beam - elasto-plastic theory approach

Timber is one of engineering materials that behaves elasto-plastic property. However, the number of research that considers the elasto-plastic property of timber to analyse or to predict ultimate load of timber beam is limited. The application of perfectly elasto-plastic property for timber is proposed to predict the ultimate strength of solid and glulam beams. Three yield criteria for timber are introduced, i.e. yield criterion I, II and III. All criteria are developed based on orthotropic and microstructure property of timber. The existing criteria proposed by Tsai-Wu and Hill are also considered. These criteria were used to develop the theoretical model in order to predict the ultimate load of timber beams (solid and glulam). The ultimate loads predicted by perfectly elasto-plastic model (using yield criterion III) are in close agreement with experimental results. The predicted load-deflection curves using perfectly elasto-plastic model (using yield criterion III) is found to be approaching experimental load-deflection curves for most beams. Therefore this shows that the timber can be idealised as a perfectly elasto-plastic material. It can be concluded that the yield criterion III is the best criterion for solid and glulam timber beam. This new yield criterion is significant for development of theoretical model to predict ultimate load for timber beam

An improvement of tresca’s yield criterion for the analysis of timber structure

Tresca’s criterion was develop by Tresca in 1868 by considering the material is isotropic or the material behaves equal shear strength in different direction [1]. It is a well-known yield criterion and widely used to analyse isotropic material. This criterion assumed that the material is yielding under shear stress. The yielding of material occurred when shear stresses in any direction in the material approach shear strength or a critical value. This criterion is widely used to analyse soil structure, metal etc. However, the application of Tresca's criterion to analyse timber structure is found very limite

A technique to remove second order singularity application in the boundary element method for elastoplasticity plane stress analysis

This paper presents a technique to establish the strain incremental formulation in the boundary element method applied to elastoplasticity problem. In this technique, the application of second order singularity problem is avoided, and only first order singularity problem is sufficient. The proposed technique is applied to analyse a timber beam structure at the plastic stage. The solution is compared with existing strain formulation method proposed by established publication. The result gives an improved solution compared with the existing method. The proposed technique is a simplified formulation where there is no second order singularity involved in the formulation