Self-stabilizing somersaults

We investigate the open-loop stability of a planar biped robot performing a periodic motion of forward somersaults with alternating single-leg contacts. The robot has a trunk and two actuated telescopic legs with point feet which are coupled to the trunk by actuated hinges. There is compliance and damping in the hip and in the legs. The concept of open-loop control implies that all actuators of the system receive predetermined inputs that are never altered by any feedback interference. Only with the right choice of model parameters and actuator inputs is it possible to create such self-stabilizing motions exploiting the natural stability properties of the system. These unknowns have been determined using special-purpose stability-optimization methods. The resulting motion is not only stable, but also a more efficient form of forward motion than running for the investigated robot.     

Extension of TDM-PON Standards to a Single-Fiber Ring Access Network Featuring Resilience and Service Overlay

A novel single-fiber ring-tree topology overlying multiple time-division-multiplexed (TDM) passive optical networks is presented and demonstrated. Each TDM service is overlaid on a different wavelength-division-multiplexing channel. A concatenation of advanced coupler-based remote nodes (RNs) distributes the channels in an optimal geographical distribution to secondary trees, which connect to the end users. With the proposed configuration, the network features flexible deployment and provides resilience capabilities in case of a fiber cut. To compensate power losses and fulfill ITU-T G.984/IEEE 802.3ah recommendations in terms of power budget (PB) and sensitivity, remote amplification is implemented at the RNs. This technique amplifies the dropped wavelengths at each RN while keeping a totally passive outside plant. A PB study, together with optical transmission experiments and network dimensioning simulations, demonstrates the feasibility of the network design.     

Platform level support for high throughput edge applications: the Twin Cities prototype

Even in the face of increasing network bandwidth, there is a desire among service providers to improve network security, availability, and performance. These improvements require increasingly complex computations on network packets. Current networking platforms cannot keep up, leading to less than desired throughput or functionality. Network processors deliver high networking throughput, but not the complex processing capabilities required. High-performance general-purpose processors deliver the complex processing needed, but not the network throughput. Combination platforms that include high-performance general-purpose CPUs and network processors hold the promise of greatly increasing platform performance, enabling desired edge application improvements. This article presents Twin Cities, a heterogeneous multiprocessor research platform we have constructed from a standard IXP1240 platform, a high-volume Intel/spl reg/ Pentium/spl reg/ III processor platform, and custom hardware. This platform provides a high-performance path (high throughput, low latency) between the two processors and presents a shared memory model to the programmer. We motivate and describe the Twin Cities platform, discuss the applications it targets, and present performance measurements.     

Feed horn coupled bolometer arrays for SPIRE - design, simulations, and measurements

In this paper, we present the design, modeling, and measurements of feed horn coupled large bolometer arrays being developed for the Herschel Space Observatory's Spectral and Photometric Imaging REceiver (SPIRE) instrument. SPIRE has five arrays of feed horn coupled silicon-nitride micromesh "spider-web" bolometers in two instruments, a three-band photometer, and a two-band Fourier transform spectrometer, each covering the 430-GHz-1.5-THz band. The optical coupling efficiency, bandwidth, and crosstalk between adjacent pixels of the arrays were investigated with numerical electromagnetic-field simulators, and prototype arrays were measured extensively in a test facility. The measured results were found to be in good agreement with simulation predictions, and the simulation results were used as a benchmark for the design goals of the instrument.     

Carbon Aerogels as Electrode Material in Supercapacitors

Due to their large specific surface area and their high electrical conductivity carbon aerogels are promising materials for electrodes in electrochemical double-layer capacitors (supercapacitor). The carbon aerogels were made via pyrolysis of resorcinol formaldehyde aerogels. The latter were prepared by supercritical and subcritical drying as well. The important findings of our investigation were, that the highest capacities of 46 F/cm³ were measured for samples with a density of about 800 kg/m³ pyrolyzed at 800°C. Also it was shown that RF-gels with molar resorcinol/catalyst ratios 1000 or higher can be dried subcritically without cracking or significant shrinkage. Carbon aerogels derived from these RF-aerogels have a small mesopore surface area, however an especially large micropore area. They provide electrical capacities which are most suitable for their use in supercapacitors.     

Impact of Backup Power in Optimizing Deployment Cost of Hybrid Optical Wireless Broadband Access Network (HOWBAN) with Survivability

Wireless Personal Communications - The dependence on broadband to enhance the economy and environment sustainability is imposing immense urgency to provide ubiquitous wireless broadband access...     

In Vitro hydrodynamic evaluation of prosthetic polymer heart valves in steady flow

Hydrodynamic comparison of two polymer valves with two mechanical valves is presented. The valves were perfused in a steady flow system, and comparisons between the valves were made on the transvalvular pressure distribution and drop, opening area, and leakage volume. Particular emphasis was placed on a slit-type bileaflet polymer valve which was newly designed and fabricated in our research group. The results showed that the functional characteristics of a slit-type bileaflet polymer valve compared favorably with that of mechanical valves. This valve may be a viable and inexpensive alternative, especially for short-term use in TAH or VAD systems.     

Effect of position and height of a mobile core type artificial disc on the biomechanical behaviour of the lumbar spine

The extent of natural disc removal and the implant position and height of an artificial disc with a mobile core were studied for their effects on intersegmental rotation, intradiscal pressure, and facet joint force. A validated finite element model of the lumbar spine was used. The model was loaded with the upper body weight, a follower load, and muscle forces to simulate standing, flexion, extension, lateral bending, and axial rotation. The implant position was varied up to 2 mm in an anterior and posterior direction and up to 3 mm in a lateral direction. Three different implant heights were simulated. The effect of removing the lateral parts of the annulus was also studied. The implant position and height markedly affect intersegmental rotation and facet joint forces but have hardly any influence on intradiscal pressure in the adjacent discs. Removing the lateral parts of the annulus increases intersegmental rotation and facet joint force mainly for lateral bending and axial rotation. The calculated translation of the mobile implant core is about 1 mm at most, and thus its effect is often overestimated. Great care should be taken to choose the optimal implant height and to insert the implant in the best position for each individual patient.     

Online Signal Injection Through a Bus-Referenced Current Transformer

An online signal injection approach based on a special current transformer is proposed as part of a solution for improving the test setup of transfer function diagnostics of transformers. However, the method is general and applicable to many types of substation equipment, such as circuit breakers and transmission lines. The system allows a high-power, high-frequency test signal to be injected directly on a high-voltage bus of an energized system. Due to the self-contained nature of the injector, no external power supplies or signal generators are needed and the design does not need to be ground-referenced. The system can thus be at the bus potential. In conjunction with wireless communication for control, no isolator bushings are required and the device can be constructed as a sleeve to be mounted around the busbar. This allows for economical retrofitting to existing installations. In this paper, the operational need for such an injection device is discussed, followed by the theory behind the proposed concept. Finally, a low-voltage, optically controlled, self-powered prototype is designed and demonstrated online to show the practical validity of the concept.