Performance Comparison of Handover Rerouting Schemes in Wireless ATM Networks

The major issue of the integration of wireless and wired ATM is the support of user mobility. In effect, many technical challenges have been posed due to mobility support. One of the most important challenges is the rerouting of active connections of mobile user during handover. The rerouting of connections must exhibit low handover latency, limit the handover delay or disruption time, maintain efficient routes and minimise the impact on existing infrastructure. To date, two dominant approaches have been proposed to support mobility into fixed ATM network. The first is the mobility enhanced switches approach and the second is the separate network-elements specific to mobility approach. The first approach implies updating the existing ATM switches with mobile specific features. The mobility functions in the second approach are entrusted to a control station attached to the ATM switch as is implemented by the Magic WAND projects. In this thesis, we investigate how mobility can be supported using both approaches. To demonstrate the effectiveness of the above approaches, we compare the performance by analytically derived formulate for their hand over latency, hand over delay, buffer size, and bandwidth requirements. The formulate were derived for both backward and forward hand overs using a number of potential rerouting schemes proposed for wireless ATM network. The results show that the mobility enhanced switches approach has slightly better performance than the separate network elements approach. The results also show that backward handover has better performance than forward handover in terms of the handover delay and buffer requirement. Finally, the results show that the Anchor Switch rerouting scheme is the best among other rerouting schemes proposed for wireless ATM

Crushing Behaviour of Woven Roving Glass Fibre/Epoxy Laminated Composite Rectangular Tubes Subjected to 'Quasi-Static Compressive Load

The automotive industry is exploring to adapting more fibre reinforced composite materials due to their stiffness to weight ratio. The amount of energy that a vehicle absorbs during a collision is a matter of concern to ensure safer and more reliable vehicle. The efficient use of composite material in the field of crash worthiness depends on the understanding of how a composite member absorbs and dissipates energy during the event of an impact. An experimental and finite element investigation of the woven roving glass fibre/epoxy laminated composite rectangular tubes subjected to compressive loading were carried out under compressive loading. Through out this investigation, rectangular tubes with different cross-sectional aspect ratio varying (alb) from 1 to 2 with 0.25 increment were investigated under axial and lateral loading conditions applied independently. The effects of increasing the cross-sectional aspect ratio on the load carrying capacity and the energy absorption capability were also presented and discussed. Finite element models to predict the load carrying capacity, failure mechanism and stress contours at pre-crush stage of the rectangular tubes under axial and lateral loading conditions have been developed. Experimental results show that the cross-sectional aspect ratio significantly affects the load carrying capacity and the energy absorption capability of the tubes. The axially loaded rectangular tubes have better load carrying capacity and energy absorption capability compared to the laterally loaded rectangular tubes. The buckling failure mode has been identified for the rectangular tubes under the different loading conditions. The developed finite element models approximately predict the initial failure load and the deformed shapes. The discrepancy between the finite element prediction and the experimental results is due to the assumption made in the finite element models and not considering the imperfection of the real tubes in the finite element models. From the experimental and finite element results 'knockdown' factors have been proposed to be used in the design phase of energy absorption elements to predict the initial failure load

Properties of Low-Lying Heavy-Light Mesons

We present preliminary results for the B meson decay constant and masses of low-lying heavy-light mesons in the static limit. Calculations were performed on the lattice in the quenched approximation using multistate smearing functions generated from a Hamiltonian for a spinless relativistic quark. The 2S--1S and 1P--1S mass splittings are measured. Using the 1P--1S charmonium splitting to set the overall scale, the ground state decay constant, f_B, is 319 +- 11 (stat) MeV.Comment: 8 pages, 9 figures, UCLA/92/TEP/4

Semileptonic D->pi/K and B->pi/D decays in 2+1 flavor lattice QCD

We present results for form factors of semileptonic decays of $D$ and $B$ mesons in 2+1 flavor lattice QCD using the MILC gauge configurations. With an improved staggered action for light quarks, we successfully reduce the systematic error from the chiral extrapolation. The results for $D$ decays are in agreement with experimental ones. The results for B decays are preliminary. Combining our results with experimental branching ratios, we then obtain the CKM matrix elements $|V_{cd}|$, $|V_{cs}|$, $|V_{cb}|$ and $|V_{ub}|$. We also check CKM unitarity, for the first time, using only lattice QCD as the theoretical input.Comment: Talk presented at Lattice2004(heavy); 3 pages, 3 figure

Heavy Quark Physics in Nf=2 QCD

We present a preliminary analysis of the heavy-heavy spectrum and heavy-light decay constants in full QCD, using a tadpole-improved SW quark action and an RG-improved gauge action on a 16^3 x 32 lattice with four sea quark masses corresponding to m_pi/m_rho = 0.8, 0.75, 0.7, 0.6 and a^-1 = 1.3 GeV. We focus particularly on the effect of sea quarks on these observables.Comment: 3 pages Latex, 3 eps figures. Uses espcrc2.sty and epsf.sty . To appear in the Proceedings of Lattice 98 (Heavy Quarks