Showing papers by "Karlsruhe Institute of Technology published in 2009"

Gold Helix Photonic Metamaterial as Broadband Circular Polarizer

Abstract: We investigated propagation of light through a uniaxial photonic metamaterial composed of three-dimensional gold helices arranged on a two-dimensional square lattice. These nanostructures are fabricated via an approach based on direct laser writing into a positive-tone photoresist followed by electrochemical deposition of gold. For propagation of light along the helix axis, the structure blocks the circular polarization with the same handedness as the helices, whereas it transmits the other, for a frequency range exceeding one octave. The structure is scalable to other frequency ranges and can be used as a compact broadband circular polarizer.

A tissue-scale gradient of hydrogen peroxide mediates rapid wound detection in zebrafish

Abstract: Barrier structures (for example, epithelia around tissues and plasma membranes around cells) are required for internal homeostasis and protection from pathogens. Wound detection and healing represent a dormant morphogenetic program that can be rapidly executed to restore barrier integrity and tissue homeostasis. In animals, initial steps include recruitment of leukocytes to the site of injury across distances of hundreds of micrometres within minutes of wounding. The spatial signals that direct this immediate tissue response are unknown. Owing to their fast diffusion and versatile biological activities, reactive oxygen species, including hydrogen peroxide (H(2)O(2)), are interesting candidates for wound-to-leukocyte signalling. Here we probe the role of H(2)O(2) during the early events of wound responses in zebrafish larvae expressing a genetically encoded H(2)O(2) sensor. This reporter revealed a sustained rise in H(2)O(2) concentration at the wound margin, starting approximately 3 min after wounding and peaking at approximately 20 min, which extended approximately 100-200 microm into the tail-fin epithelium as a decreasing concentration gradient. Using pharmacological and genetic inhibition, we show that this gradient is created by dual oxidase (Duox), and that it is required for rapid recruitment of leukocytes to the wound. This is the first observation, to our knowledge, of a tissue-scale H(2)O(2) pattern, and the first evidence that H(2)O(2) signals to leukocytes in tissues, in addition to its known antiseptic role.

All-optical high-speed signal processing with silicon–organic hybrid slot waveguides

Abstract: Integrated optical circuits based on silicon-on-insulator technology are likely to become the mainstay of the photonics industry. Over recent years an impressive range of silicon-on-insulator devices has been realized, including waveguides1,2, filters3,4 and photonic-crystal devices5. However, silicon-based all-optical switching is still challenging owing to the slow dynamics of two-photon generated free carriers. Here we show that silicon–organic hybrid integration overcomes such intrinsic limitations by combining the best of two worlds, using mature CMOS processing to fabricate the waveguide, and molecular beam deposition to cover it with organic molecules that efficiently mediate all-optical interaction without introducing significant absorption. We fabricate a 4-mm-long silicon–organic hybrid waveguide with a record nonlinearity coefficient of γ ≈ 1 × 105 W−1 km−1 and perform all-optical demultiplexing of 170.8 Gb s−1 to 42.7 Gb s−1. This is—to the best of our knowledge—the fastest silicon photonic optical signal processing demonstrated. A silicon–organic hybrid slot waveguide with a strong optical nonlinearity is demonstrated to perform ultrafast all-optical demultiplexing of high-bit-rate data streams. The approach could form the basis of compact high-speed optical processing units for future communication networks.

Mobility models for vehicular ad hoc networks: a survey and taxonomy

Abstract: Vehicular Ad-hoc Networks (VANETs) have been recently attracting an increasing attention from both research and industry communities. One of the challenges posed by the study of VANETs is the definition of a vehicular mobility model providing an accurate and realistic vehicular mobility description at both macroscopic and microscopic levels. Another challenge is to be able to dynamically alter this vehicular mobility as a consequence of the vehicular communication protocols. Many mobility models have been developed by the community in order to solve these two issues. However, due to the large number of available models claiming to be adapted to vehicular traffic, and also due to their different and somehow incomparable features, understanding their true characteristics, their degree of realism with respect to vehicular mobility, and real capabilities is a hard task. In this survey, we first introduce a framework that proposes a guideline for the generation of vehicular mobility models. Then, we illustrate the different approaches chosen by the community for the development of vehicular mobility models and their interactions with network simulators. Finally, we propose an overview and taxonomy of a large range of mobility models available for vehicular ad hoc networks. The objective is to provide readers with a guideline to easily understand and objectively compare the different models, and eventually identify the one required for their needs.

Learning and generalization of motor skills by learning from demonstration

Abstract: We provide a general approach for learning robotic motor skills from human demonstration. To represent an observed movement, a non-linear differential equation is learned such that it reproduces this movement. Based on this representation, we build a library of movements by labeling each recorded movement according to task and context (e.g., grasping, placing, and releasing). Our differential equation is formulated such that generalization can be achieved simply by adapting a start and a goal parameter in the equation to the desired position values of a movement. For object manipulation, we present how our framework extends to the control of gripper orientation and finger position. The feasibility of our approach is demonstrated in simulation as well as on the Sarcos dextrous robot arm. The robot learned a pick-and-place operation and a water-serving task and could generalize these tasks to novel situations.

Design principles of photo-bioreactors for cultivation of microalgae.

Abstract: The present hype in microalgae biotechnology has shown that the topic of photobioreactors has to be revisited with respect to availability in really large scale measured in hectars footprint area, minimization of cost, auxiliary energy demand as well as maintenance and life span. This review gives an overview about present designs and the basic limiting factors which include light distribution to avoid saturation kinetics, mixing along the light gradient to make use of light/ dark cycles, aeration and mass transfer along the vertical or horizontal main axis for carbon dioxide supply and oxygen removal and last but not least the energy demand necessary to fulfil these tasks. To make comparison of the performance of different designs easier, a commented list of performance parameters is given. Based on these critical points recent developments in the areas of membranes for gas transfer and optical structures for light transfer are discussed. The fundamental starting point for the optimization of photo-bioprocesses is a detailed understanding of the interaction between the bioreactor in terms of mass and light transfer as well as the microalgae physiology in terms of light and carbon uptake kinetics and dynamics.

A quantitative fluorescence study of protein monolayer formation on colloidal nanoparticles.

Abstract: It is now known that nanoparticles, when exposed to biological fluid, become coated with proteins and other biomolecules to form a 'protein corona'. Recent systematic studies have identified various proteins that can make up this corona, but these nanoparticle-protein interactions are still poorly understood, and quantitative studies to characterize them are few in number. Here, we have quantitatively analysed the adsorption of human serum albumin onto small (10-20 nm in diameter) polymer-coated FePt and CdSe/ZnS nanoparticles by using fluorescence correlation spectroscopy. The protein corona forms a monolayer with a thickness of 3.3 nm. Proteins bind to the negatively charged nanoparticles with micromolar affinity, and time-resolved fluorescence quenching experiments show that they reside on the particle for approximately 100 s. These new findings deepen our quantitative understanding of the protein corona, which is of utmost importance in the safe application of nanoscale objects in living organisms.

Near-infrared imaging with quantum-dot-sensitized organic photodiodes

Abstract: Solution-processed photodiodes with infrared sensitivities at wavelengths beyond the bandgap of silicon (corresponding to a wavelength of ∼1,100 nm) would be a significant advance towards cost-effective imaging. Colloidal quantum dots are highly suitable as infrared absorbers for photodetection, but high quantum yields have only been reported with photoconductors1,2,3. For imaging, photodiodes are required to ensure low-power operation and compatibility to active matrix backplanes4. Organic bulk heterojunctions5 are attractive as solution-processable diodes, but are limited to use in the visible spectrum. Here, we report the fabrication and application of hybrid bulk heterojunction photodiodes containing PbS nanocrystalline quantum dots as sensitizers for near-infrared detection up to 1.8 µm, with rectification ratios of ∼6,000, minimum lifetimes of one year and external quantum efficiencies of up to 51%. By integration of the solution-processed devices on amorphous silicon active matrix backplanes, we demonstrate for the first time near-infrared imaging with organic/inorganic hybrid photodiodes. Near-infrared imaging with solution-processed organic–inorganic hybrid photodiodes is demonstrated for the first time. The hybrid bulk-heterojunction photodiodes contain PbS nanocrystalline quantum dots as sensitizers for the detection of light of up to 1.8 µm in wavelength, have a minimum lifetime of one year, and external quantum efficiencies of up to 51%.

Vehicle-to-Vehicle Communication: Fair Transmit Power Control for Safety-Critical Information

Abstract: Direct radio-based vehicle-to-vehicle communication can help prevent accidents by providing accurate and up-to-date local status and hazard information to the driver. In this paper, we assume that two types of messages are used for traffic safety-related communication: 1) Periodic messages (ldquobeaconsrdquo) that are sent by all vehicles to inform their neighbors about their current status (i.e., position) and 2) event-driven messages that are sent whenever a hazard has been detected. In IEEE 802.11 distributed-coordination-function-based vehicular networks, interferences and packet collisions can lead to the failure of the reception of safety-critical information, in particular when the beaconing load leads to an almost-saturated channel, as it could easily happen in many critical vehicular traffic conditions. In this paper, we demonstrate the importance of transmit power control to avoid saturated channel conditions and ensure the best use of the channel for safety-related purposes. We propose a distributed transmit power control method based on a strict fairness criterion, i.e., distributed fair power adjustment for vehicular environments (D-FPAV), to control the load of periodic messages on the channel. The benefits are twofold: 1) The bandwidth is made available for higher priority data like dissemination of warnings, and 2) beacons from different vehicles are treated with ldquoequal rights,rdquo and therefore, the best possible reception under the available bandwidth constraints is ensured. We formally prove the fairness of the proposed approach. Then, we make use of the ns-2 simulator that was significantly enhanced by realistic highway mobility patterns, improved radio propagation, receiver models, and the IEEE 802.11p specifications to show the beneficial impact of D-FPAV for safety-related communications. We finally put forward a method, i.e., emergency message dissemination for vehicular environments (EMDV), for fast and effective multihop information dissemination of event-driven messages and show that EMDV benefits of the beaconing load control provided by D-FPAV with respect to both probability of reception and latency.

Experimental observations of stress-driven grain boundary migration.

Abstract: In crystalline materials, plastic deformation occurs by the motion of dislocations, and the regions between individual crystallites, called grain boundaries, act as obstacles to dislocation motion. Grain boundaries are widely envisaged to be mechanically static structures, but this report outlines an experimental investigation of stress-driven grain boundary migration manifested as grain growth in nanocrystalline aluminum thin films. Specimens fabricated with specially designed stress and strain concentrators are used to uncover the relative importance of these parameters on grain growth. In contrast to traditional descriptions of grain boundaries as stationary obstacles to dislocation-based plasticity, the results of this study indicate that shear stresses drive grain boundaries to move in a manner consistent with recent molecular dynamics simulations and theoretical predictions of coupled grain boundary migration.

Engineering Route Planning Algorithms

Abstract: Algorithms for route planning in transportation networks have recently undergone a rapid development, leading to methods that are up to three million times faster than Dijkstra's algorithm. We give an overview of the techniques enabling this development and point out frontiers of ongoing research on more challenging variants of the problem that include dynamically changing networks, time-dependent routing, and flexible objective functions.

Cloud Computing – A Classification, Business Models, and Research Directions

Abstract: Lately, a new computing paradigm has emerged: “Cloud Computing”. It seems to be promoted as heavily as the “Grid” was a few years ago, causing broad discussions on the differences between Grid and Cloud Computing. The first contribution of this paper is thus a detailed discussion about the different characteristics of Grid Computing and Cloud Computing. This technical classification allows for a well-founded discussion of the business opportunities of the Cloud Computing paradigm. To this end, this paper first presents a business model framework for Clouds. It subsequently reviews and classifies current Cloud offerings in the light of this framework. Finally, this paper discusses challenges that have to be mastered in order to make the Cloud vision come true and points to promising areas for future research.

Ecological momentary assessment of mood disorders and mood dysregulation.

Abstract: In this review, we discuss ecological momentary assessment (EMA) studies on mood disorders and mood dysregulation, illustrating 6 major benefits of the EMA approach to clinical assessment: (a) Real-time assessments increase accuracy and minimize retrospective bias; (b) repeated assessments can reveal dynamic processes; (c) multimodal assessments can integrate psychological, physiological, and behavioral data; (d) setting- or context-specific relationships of symptoms or behaviors can be identified; (e) interactive feedback can be provided in real time; and (f) assessments in real-life situations enhance generalizability. In the context of mood disorders and mood dysregulation, we demonstrate that EMA can address specific research questions better than laboratory or questionnaire studies. However, before clinicians and researchers can fully realize these benefits, sets of standardized e-diary questionnaires and time sampling protocols must be developed that are reliable, valid, and sensitive to change.

Using experience sampling methods/ecological momentary assessment (ESM/EMA) in clinical assessment and clinical research: introduction to the special section.

Abstract: This article introduces the special section on experience sampling methods and ecological momentary assessment in clinical assessment. We review the conceptual basis for experience sampling methods (ESM; Csikszentmihalyi & Larson, 1987) and ecological momentary assessment (EMA; Stone & Shiffman, 1994). Next, we highlight several advantageous features of ESM/EMA as applied to psychological assessment and clinical research. We provide a brief overview of the articles in this special section, each of which focuses on 1 of the following major classes of psychological disorders: mood disorders and mood dysregulation (Ebner-Priemer & Trull, 2009), anxiety disorders (Alpers, 2009), substance use disorders (Shiffman, 2009), and psychosis (Oorschot, Kwapil, Delespaul, & Myin-Germeys, 2009). Finally, we discuss prospects, future challenges, and limitations of ESM/EMA.

The third pillar of bacterial signal transduction: classification of the extracytoplasmic function (ECF) σ factor protein family

Abstract: The ability of a bacterial cell to monitor and adaptively respond to its environment is crucial for survival. After one- and two-component systems, extracytoplasmic function (ECF) sigma factors - the largest group of alternative sigma factors - represent the third fundamental mechanism of bacterial signal transduction, with about six such regulators on average per bacterial genome. Together with their cognate anti-sigma factors, they represent a highly modular design that primarily facilitates transmembrane signal transduction. A comprehensive analysis of the ECF sigma factor protein family identified more than 40 distinct major groups of ECF sigma factors. The functional relevance of this classification is supported by the sequence similarity and domain architecture of cognate anti-sigma factors, genomic context conservation, and potential target promoter motifs. Moreover, this phylogenetic analysis revealed unique features indicating novel mechanisms of ECF-mediated signal transduction. This classification, together with the web tool ECFfinder and the information stored in the Microbial Signal Transduction (MiST) database, provides a comprehensive resource for the analysis of ECF sigma factor-dependent gene regulation.

General overview: European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) - integrating aerosol research from nano to global scales

Abstract: In this paper we describe and summarize the main achievements of the European Aerosol Cloud Climate and Air Quality Interactions project (EUCAARI). EUCAARI started on 1 January 2007 and ended on 31 December 2010 leaving a rich legacy including: (a) a comprehensive database with a year of observations of the physical, chemical and optical properties of aerosol particles over Europe, (b) comprehensive aerosol measurements in four developing countries, (c) a database of airborne measurements of aerosols and clouds over Europe during May 2008, (d) comprehensive modeling tools to study aerosol processes fron nano to global scale and their effects on climate and air quality. In addition a new Pan-European aerosol emissions inventory was developed and evaluated, a new cluster spectrometer was built and tested in the field and several new aerosol parameterizations and computations modules for chemical transport and global climate models were developed and evaluated. These achievements and related studies have substantially improved our understanding and reduced the uncertainties of aerosol radiative forcing and air quality-climate interactions. The EUCAARI results can be utilized in European and global environmental policy to assess the aerosol impacts and the corresponding abatement strategies.

Ca2+ Regulates Reactive Oxygen Species Production and pH during Mechanosensing in Arabidopsis Roots

Abstract: Mechanical stimulation of plants triggers a cytoplasmic Ca2+ increase that is thought to link the touch stimulus to appropriate growth responses. We found that in roots of Arabidopsis thaliana, external and endogenously generated mechanical forces consistently trigger rapid and transient increases in cytosolic Ca2+ and that the signatures of these Ca2+ transients are stimulus specific. Mechanical stimulation likewise elicited an apoplastic alkalinization and cytoplasmic acidification as well as apoplastic reactive oxygen species (ROS) production. These responses showed the same kinetics as mechanically induced Ca2+ transients and could be elicited in the absence of a mechanical stimulus by artificially increasing Ca2+ concentrations. Both pH changes and ROS production were inhibited by pretreatment with a Ca2+ channel blocker, which also inhibited mechanically induced elevations in cytosolic Ca2+. In trichoblasts of the Arabidopsis root hair defective2 mutant, which lacks a functional NADPH oxidase RBOH C, touch stimulation still triggered pH changes but not the local increase in ROS production seen in wild-type plants. Thus, mechanical stimulation likely elicits Ca2+-dependent activation of RBOH C, resulting in ROS production to the cell wall. This ROS production appears to be coordinated with intra- and extracellular pH changes through the same mechanically induced cytosolic Ca2+ transient.

Segmentation of 3D lidar data in non-flat urban environments using a local convexity criterion

Abstract: Present object detection methods working on 3D range data are so far either optimized for unstructured offroad environments or flat urban environments. We present a fast algorithm able to deal with tremendous amounts of 3D Lidar measurements. It uses a graph-based approach to segment ground and objects from 3D lidar scans using a novel unified, generic criterion based on local convexity measures. Experiments show good results in urban environments including smoothly bended road surfaces.

Quark and Gluon Form Factors to Three Loops

Abstract: We compute the form factors of the photon-quark-anti-quark vertex and the effective vertex of a Higgs-boson and two gluons to three-loop order within massless perturbative quantum chromodynamics. These results provide building blocks for many third-order cross sections. Furthermore, this is the first calculation of complete three-loop vertex corrections.

Thermal Conductivity and Viscosity Measurements of Water-Based TiO2 Nanofluids

Abstract: In this study, the thermal conductivity and viscosity of TiO2 nanoparticles in deionized water were investigated up to a volume fraction of 3% of particles. The nanofluid was prepared by dispersing TiO2 nanoparticles in deionized water by using ultrasonic equipment. The mean diameter of TiO2 nanoparticles was 21 nm. While the thermal conductivity of nanofluids has been measured in general using conventional techniques such as the transient hot-wire method, this work presents the application of the 3ω method for measuring the thermal conductivity. The 3ω method was validated by measuring the thermal conductivity of pure fluids (water, methanol, ethanol, and ethylene glycol), yielding accurate values within 2%. Following this validation, the effective thermal conductivity of TiO2 nanoparticles in deionized water was measured at temperatures of 13 °C, 23 °C, 40 °C, and 55 °C. The experimental results showed that the thermal conductivity increases with an increase of particle volume fraction, and the enhancement was observed to be 7.4% over the base fluid for a nanofluid with 3% volume fraction of TiO2 nanoparticles at 13 °C. The increase in viscosity with the increase of particle volume fraction was much more than predicted by the Einstein model. From this research, it seems that the increase in the nanofluid viscosity is larger than the enhancement in the thermal conductivity.

An OFDM System Concept for Joint Radar and Communications Operations

Abstract: In this paper the possibility of designing an OFDM system for simultaneous radar and communications operations is discussed. A novel approach to OFDM radar processing is introduced that overcomes the typical drawbacks of correlation based processing. A suitable OFDM system parameterization for operation at 24 GHz is derived that fulfills the requirements for both applications. The operability of the proposed system concept is verified with MatLab simulations. Keywords-OFDM; Radar, Communications

Strong optical activity from twisted-cross photonic metamaterials

Abstract: Following a recent theoretical suggestion and microwave experiments, we fabricate photonic metamaterials composed of pairs of twisted gold crosses using two successive electron-beam-lithography steps and intermediate planarization via a spin-on dielectric. The resulting two effective resonances of the coupled system lie in the 1-2 microm wavelength regime and exhibit pronounced circular dichroism, while the circular polarization conversion is very small. In between the two resonances, we find a fairly broad spectral regime with strong optical activity, i.e., with a pure rotation of incident linear polarization. The measured optical transmittance spectra agree well with theory.

Observation of Electroweak Single Top-Quark Production

Abstract: We report the observation of single top-quark production using 3.2 fb{sup -1} of pp collision data with sq root(s)=1.96 TeV collected by the Collider Detector at Fermilab. The significance of the observed data is 5.0 standard deviations, and the expected sensitivity for standard model production and decay is in excess of 5.9 standard deviations. Assuming m{sub t}=175 GeV/c{sup 2}, we measure a cross section of 2.3{sub -0.5}{sup +0.6}(stat+syst) pb, extract the CKM matrix-element value |V{sub tb}|=0.91+-0.11(stat+syst)+-0.07(theory), and set the limit |V{sub tb}|>0.71 at the 95% C.L.