A temperature controlled liquid crystal lens for spherical aberration compensation

A temperature controlled liquid crystal lens for spherical aberration compensation in a Blu-ray optical pickup is demonstrated and the influence of the temperature on the switching time is investigated. Using the liquid crystal BL-006, the shortest switching time is achieved at a temperature of 70°C, which corresponds to a reduction by a factor of 3 compared to 30°C. An optimum lens design would bring the switching time down to 320 ms, assuming a data-layer separation of 20 μm and an aperture diameter of 4 mm.     

MARKET-BASED APPROACHES TO OPTIMIZATION

We present a general discussion of what constitutes a market-oriented approach to optimization. We demonstrate how a general framework can be used to conceptually improve two well-known approaches from the literature, and discuss computational properties of the different approaches. We also show how existing theory could be adjusted to be directly applicable to the theory of the two approaches, thus proving special theory unnecessary. We want to bring out the pedagogical aspects of market mechanisms, to take full advantage of its potential.     

A quality-of-service signaling architecture for seamless handover support in next generation,IP-based mobile networks

The coupling of signaling protocols for mobility management and resource reservation plays an important role to achieve Quality-of-Service (QoS) in wireless environments. When performing a handover, request and allocation of resources have to be done in the shortest possible time to avoid disruptions for the user service. Therefore, it is preferable to ensure resource availability in advance, which we call anticipated handover. This approach for providing seamless handovers in turn poses challenges for the overall design of the QoS architecture and its associated QoS signaling protocol. This article describes the design, implementation, and evaluation of a comprehensive QoS architecture and a suitable QoS signaling protocol. It discusses intrinsic problems of reservations in IP based networks such as session ownership as well as a number of protocol design issues regarding the integration of QoS signaling with other protocols, such as Mobile IP. In particular, we define an end-to-end QoS architecture and a mobility-aware reservation signaling protocol Mobility Aware Reservation Signaling Protocol (MARSP) that supports anticipated handover, thus enabling seamless services over heterogeneous wireless access networks. The presented architecture and protocol were implemented and evaluated by measurements. They show that anticipated handovers not only outperform hard handovers regarding handover latency, but that they also provide functional and robustness advantages. Authors Hillebrand and Prehofer changed their affiliation in the meantime, the work described in this paper was carried out during their employment at DoCoMo Communications Laboratories Europe.     

Computer aided teaching in civil engineering materials science at the University of Stuttgart

During the past five years the Institute of Construction Materials at the University of Stuttgart (IWB) has participated in different projects concerning e-teaching. Amongst other efforts co-workers of IWB have created a set of virtual content concerning concrete technology within a German e-teaching network in civil engineering materials science called “WiBA-Net” (). The content of this network consists of teaching material that is organized at four different levels of granularity. At the most basic level single items (“assets”) are collected. At the second level such assets are arranged into single pages filling one screen. Several pages dealing with aspects of a single topic are ordered into a teaching path at the third level and finally a set of teaching paths forms an entire course at level four. Virtual searching methods are offered on all four levels depending on the state of the user. Besides the mentioned teaching material also virtual communication facilities are offered within the network. During the work on WiBA-Net, which consists of six German Universities, questions concerning the reusability of virtual content, metadata enhancement techniques and the concept of Blended Learning were focused. Educational and didactic aspects have been closely taken into account and quality assuring evaluation methods have been applied. Meanwhile first experiences have been made in real life teaching and learning situations, which give us an idea of future needs and development in the field.     

Investigations of the fundamental quantum noise properties of resonant-cavity light-emitting diodes (rcleds)

We present first results of the investigations of the quantum noise properties of resonant-cavity light-emitting diodes (rcleds). We obtain a quantum noise of up to ?0.07dB below the shot noise quantum limit already at moderate pump levels and when being pumped by a quiet current source. This amount of observed sub-shot noise emission is in accordance with the quantum efficiency of the devices. This Sub-Poisson intensity noise ofrcleds together with their narrow beam characteristics make them very attractive for applications in photonics and metrology.     

System Level Modeling of Microsystems Using Order Reduction Methods

The dynamic element matching (DEM) techniques for digital-to-analog converters(DACs) has been suggested as a promising method to improve matching between the DAC's referencelevels. However, no work has so far taken the dynamic effects that limit the performance for higher frequenciesinto account. In this paper we present a model describing the dynamic properties of a DEM DAC and compare thesimulated results with measurements of a 14-bit current-steering DEM DAC implemented in a 0.35-m CMOSprocess. The measured data agrees well with the results predicted by the used model. It is also shown that theDEM technique does not necessarily increase the performance of a DAC when dynamic errors are dominating theachievable performance.     

Nanofluidic networks based on surfactant membrane technology

We explore possibilities to construct nanoscale analytical devices based on lipid membrane technology. As a step toward this goal, we present nanotube-vesicle networks with fluidic control, where the nanotube segments reside at, or very close (<2 microm) to optically transparent surfaces. These nanofluidic systems allow controlled transport as well as LIF detection of single nanoparticles. In the weak-adhesion regime, immobilized vesicles can be approximated as perfect spheres with nanotubes attached at half the height of the vesicle in the axial (z) dimension. In the strong-adhesion regime (relative contact area, Sr* approximately 0.3), nanotubes can be adsorbed to the surface with a distance to the interior of the nanotubes defined by the membrane thickness of approximately 5 nm. Strong surface adsorption restricts nanotube self-organization, enabling networks of nanotubes with arbitrary geometries. We demonstrate LIF detection of single nanoparticles (30-nm-diameter fluorescent beads) inside single nanotubes. Transport of nanoparticles was induced by a surface tension differential applied across nanotubes using a hydrodynamic injection protocol. Controlled transport in nanotubes together with LIF detection enables construction of nanoscale fluidic devices with potential to operate with single molecules. This opens up possibilities to construct analytical platforms with characteristic length scales and volume orders of magnitudes smaller than employed in traditional microfluidic devices.     

Amperometric detection of exocytosis in an artificial synapse

A liposome model of exocytosis has been used to examine the nanometer environment of the space between the electrode and the membrane. First, this has been used to test models of coulometric efficiency for different size vesicles with 5- and 33-microm electrodes. The resulting model has a best fit that suggests that the liquid space is approximately 300 nm across the gap. Given this dimension, the volume of the electrode-membrane space is not large enough to accommodate the volume of larger vesicles in cells such as the mast cells of the beige mouse. Second, the model suggests that flow of solution from the exocytosis event is more important than diffusion. Flow from the finite vesicle volume past the electrode leads to less charge passed. Third, and finally, this system can be used to model transport in the synapse and so it is possible to examine the idea that transmitter flows in addition to diffusing from the synapse. This model should be useful in understanding and quantifying the escape of transmitter from synapses in vivo.     

Reaction kinetics in a tight spot

The standard analysis of reaction networks based on deterministic rate equations fails in confined geometries, commonly encountered in fields such as astrochemistry, thin-film growth and cell biology. In these systems the small reactant population implies anomalous behavior of reaction rates, which can be accounted for only by following the full distribution of reactant numbers.     

Toxic gas clouds: effects and implications of dry deposition on concentration

The influence of the dry deposition process on concentration pertaining to toxic gas clouds was investigated by model calculations. Three main release scenarios were simulated, with nine micrometeorological cases considered for each. To compare and confirm the results, two model types, a stochastic particle model and a box-type model, were independently used to simulate many of the different cases. The results showed that the effects of dry deposition may be strong for releases at, or confined close to the ground, e.g. neutral or unstable stratification can cause higher concentrations than stable stratification after 10-15 km. Risk distances are in turn affected and may be substantially shortened, e.g. for a zero-height release like that from an evaporating pool, a 50% reduction in total airborne substance may occur within 500 m at a low wind velocity and neutral or stable stratification.