Equivalent random analysis of a buffered optical switch with general interarrival times

We propose an approximate analytic model of an optical switch with fibre delay lines and wavelength converters by employing Equivalent Random Theory. General arrival traffic is modelled by means of Gamma-distributed interarrival times. The analysis is formulated in terms of virtual traffic flows within the optical switch from which we derive expressions for burst blocking probability, fibre delay line occupancy and mean delay. Emphasis is on approximations that give good numerical efficiency so that the method can be useful for formulating dimensioning problems for large-scale networks. Numerical solution values from the proposed analysis method compare well with results from a discrete-event simulation of an optical burst switch

Characterisation, Modelling and Simulation of Flexible Polyurethane Foam

Flexible polyurethane foam is an open-celled polymeric material that exhibits strain rate and temperature effects. It has found various applications in areas including the packaging, medical, sports, aerospace and aeronautical industries. Polyurethane foam is ubiquitous in seating applications and finds particular use in specialised wheelchair seating where customised seating solutions are required which can provide proper comfort and support without the risk of developing pressure ulcers. Proper seating design is critical for users if this problem is to be avoided, but a lack of quantitative knowledge of this material’s behaviour has limited its effectiveness. The objectives of the work presented here are twofold. Firstly to characterise the behaviour of the materials and secondly to develop a validated numerical model which can be used to increase understanding of in-service behaviour. Three commonly used foams having different densities and viscoelastic properties were subjected to compression in a uni-axial test machine fitted with a custom-built temperature chamber. The results of these tests were analysed and are presented to aid in the characterisation of these materials. The effects on the stiffness of foam of different additives, densities, strain rates and temperatures were noted. A material model was developed to simulate indentation, in which compression and shear were the predominant modes of deformation. The results from the uni-axial characterisation tests were employed to determine material constants for Ogden’s constitutive model for compressible materials. Simple shear tests were also conducted with a custom-built dual lap shear tester and material constants were then determined for this mode of deformation. A curve-fit was developed which was a compromise between both modes of deformation to provide increased material model robustness. To validate the accuracy of the developed model, uni-axial indentation of standard polyurethane seating foam was then modelled using Finite Element (FE) code. Results show a high degree of accuracy

Testing, Modelling and Validation of Numerical Model Capable of Predicting Stress Fields Throughout Polyurethane Foam

Wheelchair seating systems are specialised for a number of reasons as users can have impaired mobility, which increases the possibility of pressure build up. These areas of high pressure frequently occur in the trunk region under the bony prominences known as the Ischial Tuberosities (IT), pressure ulcers may occur consequently. Polyurethane foam has been in use for some time in wheelchair seating systems as it exhibits good pressure relieving capabilities in most cases. However, little quantitative research has gone into foamed polymers, in comparison with conventional elastomeric materials. This lack of knowledge can ultimately lead to more time being spent in fitting, increased possibility of refitting and potentially an increase in trunk region pressures leading to the development of ulcers. Test results were used to accurately validate a Visco-Hyperfoam material model. Accurately simulating an indentation procedure using FE software verified the validation of the material model

Prediction of Compressive Creep Bhaviour in Flexible Polyurethane Foam Over Long Time Scales and at Elevated Temperatures

Compressive creep gradually affects the structural performance of flexible polymeric foam material over extended time periods. When designing components, it is often difficult to account for long-term creep, as accurate creep data over long time periods or at high temperatures is often unavailable. This is mainly due to the lengthy testing times and/or inadequate high temperature testing facilities. This issue can be resolved by conducting a range of short-term creep tests and applying accurate prediction methods to the results. Short-term creep testing was conducted on viscoelastic polyurethane foam, a material commonly used in seating and bedding systems. Tests were conducted over a range of temperatures, providing the necessary results to allow for the generation of predictions of long-term creep behaviour using time-temperature superposition. Additional predictions were generated, using the William Landel Ferry time-temperature empirical relations, for material performance at temperatures above and below the reference temperature range. Further tests validated the results generated from these theoretical predictions

The Implementation of a Visco-hyperelastic Numerical Material Model for Simulating the Behaviour of Polymer Foam Materials

Polyurethane foam has been in use for some time in wheelchair seating systems as it offers good pressure relieving capabilities in most cases. However, little characterisation work has gone into seating foam materials by comparison with conventional elastomeric materials. Accurate material models could allow better prediction of foam in-service behaviour, which could potentially improve seating design practises. The objective of this work was to develop an approach for the validation of hyperelastic and viscoelastic material model parameters used to simulate polyurethane foam behaviour. Material parameters were identified from relevant test procedures and implemented in a Finite Element simulation of an ISO foam indentation procedure. Physical test results were compared to results predicted using the identified material parameters. Simulations suggest a good overall agreement between test and model results

An Exploratory Study of the Effects of Aquatic Walking on Function and Muscle Activity in Knee Osteoarthritis: Part 2

This paper presents Part 2 of a study that investigated the effects of an 8-week (3x/week) underwater treadmill (UT) walking intervention on knee osteoarthritis (KOA) outcomes in 6 adults with KOA (62.7 ± 14.2 years). The Knee Outcome Survey (KOS) for activities of daily living and muscle activity during a 10-m walk and a 20 cm step down were measured before and after the intervention. The following KOS measures improved after the UT walking program (p \u3c 0.05; g \u3e 0.8): stiffness, swelling, weakness, walking, going up stairs, going downstairs, kneeling on the front of the knee, squatting, and sitting with the knee bent. Knee flexion excursion during stance of walking increased after the UT walking intervention (p = .01). Co-activation between the tibialis anterior and medial gastrocnemius decreased during the 20 cm step down (p = .04). The findings of this study support using the WWE as a model for UT walking interventions in KOA

Mobile Operator Publishing and Entertainment Platform

There is a gap between mobile Operators and content Publishers, hindering established small and medium sized publishers to enter the mobile market despite its commercial potential. A Mobile Operator Publishing and Entertainment Platform enables the creation of a new category of mobile service called a mobile magazine. An m-Mag (mobile magazine) is a next generation mobile publishing service that is made available from a mobile operator's portal, that is integrated with value added mobile data services and that uses the operator's billing capabilities to charge consumers for access to the magazine. Using Parlay/OSA as an open approach, the m-Mag platform can integrate into an operator's network using standardised APIs and is portable across different operator networks

AgileDCN:An Agile Reconfigurable Optical Data Center Network Architecture

This paper presents a detailed examination of a novel data center network (DCN) that can satisfy the high capacity and low latency requirements of modern cloud computing applications. This reconfigurable architecture called AgileDCN uses fast-switching optical components with a centralized control function and workload scheduler. By providing a highly flexible optical network fabric between server racks, very high network efficiencies can be achieved even under imbalanced loading patterns. Our simulation results show that, at high (70%) loads, TCP flow completion times in the AgileDCN are significantly lower than in an equivalent electronic leaf-spine network