Constructing 3D crystal templates for photonic band gap materials using holographic optical tweezers

A simple and robust method is presented for the construction of 3-dimensional crystals from silica and polystyrene microspheres. The crystals are suitable for use as templates in the production of three-dimensional photonic band gap (PBG) materials. Manipulation of the microspheres was achieved using a dynamic holographic assembler (DHA) consisting of computer controlled holographic optical tweezers. Attachment of the microspheres was achieved by adjusting their colloidal interactions during assembly. The method is demonstrated by constructing a variety of 3-dimensional crystals using spheres ranging in size from 3 µm down to 800 nm. A major advantage of the technique is that it may be used to build structures that cannot be made using self-assembly. This is illustrated through the construction of crystals in which line defects have been deliberately included, and by building simple cubic structures

Why Value is Everything: A User-Centered Approach to Internet Quality of Service and Pricing

To create acceptable levels of Quality of Service (QoS), designers need to be able to predict users' behaviour in response to different levels of QoS. However, predicting behaviour requires an understanding of users' requirements for specific tasks and contexts. This paper reports qualitative and experimental research that demonstrates that future network service must be based on an old principle: service and its associate cost must represent value in terms of the contribution it makes to customers' goals. Human Computer Interaction (HCI) methods can be applied to identify users' goals and associated QoS requirements. Firstly, we used a qualitative approach to establish the mental concepts that users apply when assessing network services and charges

Botulinum toxin A injections do not improve surface EMG patterns during gait in children with cerebral palsy-A randomized controlled study

AbstractChildren with cerebral palsy who walk with knee flexion during midstance are treated with intramuscular injections of botulinum toxin A (BTX-A) to prevent them from potential deterioration and to improve their mobility. The present study evaluates the effect of this treatment on the muscle activation patterns of the rectus femoris, medial hamstrings and gastrocnemius medialis during gait. Twenty-two children (aged 4–11 years) with cerebral palsy, who walked with knee flexion, were randomly assigned to an intervention group (multilevel BTX-A injections combined with comprehensive rehabilitation) or a control group (usual care). Sagittal and frontal video recordings were made of gait, together with simultaneous surface electromyography recordings of the rectus femoris, medial hamstring and gastrocnemius medialis muscles, before and six weeks after treatment. Abnormal muscle activation patterns were quantified, after gain-normalisation, according to the root mean square difference (RMSD), which is the difference relative to normal patterns. Six weeks after the treatment the RMSD of the gastrocnemius medialis muscles in the intervention group changed significantly, showing a deterioration (p<0.05). This study demonstrated that BTX-A injections do not result in an improvement in lower limb muscle activation patterns during gait. In spite of this lack of direct effect on muscle activation patterns, the combination of BTX-A injections and comprehensive rehabilitation was effective in improving gait kinematics