De week van ... Romy van der Kooij

In iedere editie nemen we een kijkje in het leven van een B.I.L. lid. Dit keer vertelt Romy van der Kooij (19) over een typische week in november. Romy is eerstejaars bestuurskundestudent en is actief in de Commissie Activiteiten

Performance of TCP with multiple Priority Classes

We consider the dimensioning problem for Internet access links carrying TCP traffic with two priority classes. To this end, we study the behaviour of TCP at the flow level described by a multiple-server Processor Sharing (PS) queueing model with two customer classes, where the customers represent flows generated by downloading Internet objects; the sojourn times represent the object transfer times. We present closed-form expressions for the mean sojourn times for high-priority customers and approximate expressions for the mean sojourn times of low-priority customers. The accuracy of the model is demonstrated by comparing results based on the PS model with "real" TCP simulation results obtained by the well-known Network Simulator. The experimental results demonstrate that the model-based results are highly accurate when the mean object size is at least 10 IP-packets, and the loss rate is negligible

A Gait Rehabilitation Robot for the Training of Subtasks in Walking

Background: In the past decade, different gait rehabilitation robots have been developed. These robots concentrated on relearning gait by repeatedly enforcing a walking pattern for the whole leg or only for the foot. Such training might be less task specific as generally thought, because learning to walk is more complex than learning a position trajectory. We believe active participation of the patient in training and subdivision of the training in several subtasks leads to more comprehensive and functional training. Methods: Using a newly developed actuated exoskeleton (LOPES) in combination with a treadmill, we aimed to selectively and gently support specific subtasks of walking, like knee stabilization, lateral balance, and foot clearance. Foot clearance and knee stabilization subtask had been implemented with dedicated controllers and tested during walking with healthy subjects. Results: Foot clearance could be increased without disrupting the subject’s own initiated walking in the remainder of the gait cycle. During weight acceptation, the knee stabilization ensured by the exoskeleton while the subject relaxed his knee. The gentle control of the robot allowed a comfortable interaction between subject and robot. Conclusion: Selective support of subtasks seems to be a viable method of interaction with the patient to train his or her gait. In the near future, we will implement a complete set of gait subtasks, which makes all kinds of training interventions possible

Insulating fcc YH3-ô stabilized by MgH2

We study the structural, optical, and electrical properties of MgzY1-z switchable mirrors upon hydrogenation. It is found that the alloys disproportionate into essentially pure YH3-δ and MgH2 with the crystal structure of YH3-δ dependent on the Mg concentration z. For 0~0.1 only cubic YH3-δ is present. Interestingly, cubic YH3-δ is expanded compared to YH2, in disagreement with theoretical predictions. From optical and electrical measurements we conclude that cubic YH3-δ is a transparent insulator with properties similar to hexagonal YH3-δ. Our results are inconsistent with calculations predicting fcc YH3-δ to be metallic, but they are in good agreement with recent GW calculations on both hcp and fcc YH3. Finally, we find an increase in the effective band gap of the hydrided MgzY1-z alloys with increasing z. Possibly this is due to quantum confinement effects in the small YH3 clusters