Showing papers by "University of Paderborn published in 2013"

Three-dimensional optical holography using a plasmonic metasurface

Abstract: Holographic techniques allow for the construction of 3D images by controlling the wave front of light beams. Huang et al. develop ultrathin plasmonic metasurfaces to provide 3D optical holographic image reconstruction in the visible and near-infrared regions for circularly polarized light.

Software Engineering for Self-Adaptive Systems : A Second Research Roadmap

Abstract: The goal of this roadmap paper is to summarize the state-of-the-art and identify research challenges when developing, deploying and managing self-adaptive software systems. Instead of dealing with a wide range of topics associated with the field, we focus on four essential topics of self-adaptation: design space for self-adaptive solutions, software engineering processes for self-adaptive systems, from centralized to decentralized control, and practical run-time verification & validation for self-adaptive systems. For each topic, we present an overview, suggest future directions, and focus on selected challenges. This paper complements and extends a previous roadmap on software engineering for self-adaptive systems published in 2009 covering a different set of topics, and reflecting in part on the previous paper. This roadmap is one of the many results of the Dagstuhl Seminar 10431 on Software Engineering for Self-Adaptive Systems, which took place in October 2010.

Mesoporous materials as gas sensors

Abstract: Ordered mesoporous materials have great potential in the field of gas sensing. Today various template-assisted synthesis methods facilitate the preparation of silica (SiO2) as well as numerous metal oxides with well-defined, uniform and regular pore systems. The unique nanostructural properties of such materials are particularly useful for their application as active layers in gas sensors based on various operating principles, such as capacitive, resistive, or optical sensing. This review summarizes the basic aspects of materials synthesis, discusses some structural properties relevant in gas sensing, and gives an overview of the literature on ordered mesoporous gas sensors.

Helicity dependent directional surface plasmon polariton excitation using a metasurface with interfacial phase discontinuity

Abstract: Researchers have now demonstrated a reconfigurable, unidirectional coupling scheme for excitation of collective oscillations of the electrons at a metal surface, the so-called surface plasmon-polaritons. Lingling Huang and co-workers achieved an efficient and controllable coupling of photons in free space to these surface states on a metal film — a task important for the future development of nanoscale optoelectronic circuitry — by employing a nanostructured thin metal film on a glass substrate. The nanostructured metal film features an array of rectangular nano-apertures arranged in a carefully designed orientation and pattern. Such a ‘plasmonic metasurface’ couples photons to surface plasmon-polaritons while depending crucially on the circular polarization state of the incident light. As a result, when circularly polarized light strikes the surface, the handedness of the light dictates the propagation direction of the resulting surface plasmon-polaritons.

Helicity Dependent Directional Surface Plasmon Polariton Excitation Using A Metasurface with Interfacial Phase Discontinuity

Abstract: Surface plasmon polaritons (SPPs) have been widely exploited in various scientific communities, ranging from physics, chemistry to biology, due to the strong confinement of light to the metal surface. For many applications it is important that the free space photon can be coupled to SPPs in a controllable manner. In this Letter, we apply the concept of interfacial phase discontinuity for circularly polarizations on a metasurface to the design of a novel type of polarization dependent SPP unidirectional excitation at normal incidence. Selective unidirectional excitation of SPPs along opposite directions is experimentally demonstrated at optical frequencies by simply switching the helicity of the incident light. This approach, in conjunction with dynamic polarization modulation techniques, opens gateway towards integrated plasmonic circuits with electrically reconfigurable functionalities.

The reverb challenge: Acommon evaluation framework for dereverberation and recognition of reverberant speech

Abstract: Recently, substantial progress has been made in the field of reverberant speech signal processing, including both single- and multichannel dereverberation techniques, and automatic speech recognition (ASR) techniques robust to reverberation. To evaluate state-of-the-art algorithms and obtain new insights regarding potential future research directions, we propose a common evaluation framework including datasets, tasks, and evaluation metrics for both speech enhancement and ASR techniques. The proposed framework will be used as a common basis for the REVERB (REverberant Voice Enhancement and Recognition Benchmark) challenge. This paper describes the rationale behind the challenge, and provides a detailed description of the evaluation framework and benchmark results.

Charge noise and spin noise in a semiconductor quantum device

Abstract: Improving the quantum coherence of solid-state systems that mimic two-level atoms, for instance spin qubits or single-photon emitters using semiconductor quantum dots, involves dealing with the noise inherent to the device. Charge noise results in a fluctuating electric field, spin noise in a fluctuating magnetic field at the location of the qubit, and both can lead to dephasing and decoherence of optical and spin states. We investigate noise in an ultrapure semiconductor device using a minimally invasive, ultrasensitive local probe: resonance fluorescence from a single quantum dot. We distinguish between charge noise and spin noise through a crucial difference in their optical signatures. Noise spectra for both electric and magnetic fields are derived from 0.1 Hz to 100 kHz. The charge noise dominates at low frequencies, spin noise at high frequencies. The noise falls rapidly with increasing frequency, allowing us to demonstrate transform-limited quantum-dot optical linewidths by operating the device above 50 kHz. Charge noise and spin noise lead to decoherence of the state of a quantum dot. A fast spectroscopic technique based on resonance fluorescence can distinguish between these two deleterious effects, enabling a better understanding of how to minimize their influence.

Highly Anisotropic Steel Processed by Selective Laser Melting

Abstract: For additive manufacturing of metals, selective laser melting can be employed. The microstructure evolution is directly influenced by processing parameters. Employing a high energy laser system, samples made from austenitic stainless steel were manufactured. The microstructure obtained is characterized by an extremely high degree of anisotropy featuring coarse elongated grains and a 〈001〉 texture alongside the build direction during processing. Eventually, the anisotropy of the microstructure drastically affects the monotonic properties of the current material.

Chirality in Liquid Crystals

Abstract: Classroom Experiments with Chiral Liquid Crystals.- From a Chiral Molecule to a Chiral Anisotropic Phase.- Chemical Structures and Polymorphism.- Cholesteric Liquid Crystals: Defects and Topology.- Cholesteric Liquid Crystals: Optics, Electro-optics, and Photo-optics.- Blue Phases.- Smectic Liquid Crystals: Ferroelectric Properties and Electroclinic Effect.- Smectic Liquid Crystals: Antiferroelectric and Ferrielectric Phases.- Twist Grain Boundary Phases.- Columnar Liquid Crystals.- Some Aspects of Polymer Dispersed and Polymer Stabilized Chiral Liquid Crystals.- Chirality in Liquid Crystal Elastomers.- Phase Chirality of Micellar Lyotropic Liquid Crystals.- Traveling Phase Boundaries with the Broken Symmetries of Life.

Responsive hydrogels – structurally and dimensionally optimized smart frameworks for applications in catalysis, micro-system technology and material science

Abstract: Although the technological and scientific importance of functional polymers has been well established over the last few decades, the most recent focus that has attracted much attention has been on stimuli-responsive polymers. This group of materials is of particular interest due to its ability to respond to internal and/or external chemico-physical stimuli, which is often manifested as large macroscopic responses. Aside from scientific challenges of designing stimuli-responsive polymers, the main technological interest lies in their numerous applications ranging from catalysis through microsystem technology and chemomechanical actuators to sensors that have been extensively explored. Since the phase transition phenomenon of hydrogels is theoretically well understood advanced materials based on the predictions can be prepared. Since the volume phase transition of hydrogels is a diffusion-limited process the size of the synthesized hydrogels is an important factor. Consistent downscaling of the gel size will result in fast smart gels with sufficient response times. In order to apply smart gels in microsystems and sensors, new preparation techniques for hydrogels have to be developed. For the up-coming nanotechnology, nano-sized gels as actuating materials would be of great interest.

High Tech and High Touch: A Framework for Understanding User Attitudes and Behaviors Related to Smart Interactive Services

Abstract: Smart interactive services, in contrast with other technology-based services, require significant human-to-human interaction and collaboration in addition to the service provided by the embedded te...

Journey describing applications of oxone in synthetic chemistry

Abstract: Hidayat Hussain,*,†,‡ Ivan R. Green, and Ishtiaq Ahmed †Department of Chemistry, University of Paderborn, Warburger Strasse 100, 33098 Paderborn, Germany ‡Department of Biological Sciences and Chemistry, College of Arts and Sciences, University of Nizwa, Birkat Al-Mouz, Nizwa 616, Sultanate of Oman Department of Chemistry and Polymer Science, University of Stellenbosch, P/Bag X1Matieland 7602, South Africa Karlsruhe Institute of Technology (KIT), DFG Centre for Functional Nanostructures, Wolfgang Gaede Strasse 1, 76131 Karlsruhe, Germany

A versatile source of single photons for quantum information processing

Abstract: The generation of high-quality single-photon states with controllable narrow spectral bandwidths and central frequencies is key to facilitate efficient coupling of any atomic system to non-classical light fields. Such an interaction is essential in numerous experiments for fundamental science and applications in quantum communication and information processing, as well as in quantum metrology. Here we implement a fully tunable, narrow-band and efficient single-photon source based on a whispering gallery mode resonator. Our disk-shaped, monolithic and intrinsically stable resonator is made of lithium niobate and supports a cavity-assisted spontaneous parametric down-conversion process. The generated photon pairs are emitted into two highly tunable resonator modes. We verify wavelength tuning over 100 nm of both modes with controllable bandwidth between 7.2 and 13 MHz. Heralding of single photons yields anti-bunching with g(2)(0)<0.2.

Procrastination: When good things don’t come to those who wait.

Abstract: Procrastination is a well-known phenomenon that often entails negative outcome with regard to performance and subjective well-being. In an attempt to understand the (alarming) character of procrastination, a large body of research on the causes, correlates, and consequences of procrastination has been accumulating over the last 40 years. The aim of this paper is to provide a systematic characterization of the trends in procrastination research and to suggest future directions for research and practice. The systematic characterization comprises a comparison of procrastination to functional forms of delay (referred to as strategic delay) and a presentation of the theoretical approaches to explaining procrastination. The future directions suggested pertain to the development of a differentiated understanding of procrastination and of integral interventions.

Inconel 939 processed by selective laser melting: Effect of microstructure and temperature on the mechanical properties under static and cyclic loading

Abstract: Nickel-based superalloys, such as Inconel 939, are a long-established construction material for high-temperature applications and profound knowledge of the mechanical properties for this alloy produced by conventional techniques exists. However, many applications demand for highly complex geometries, e.g. in order to optimize the cooling capability of thermally loaded parts. Thus, additive manufacturing (AM) techniques have recently attracted substantial interest as they provide for an increased freedom of design. However, the microstructural features after AM processing are different from those after conventional processing. Thus, further research is vital for understanding the microstructure-processing relationship and its impact on the resulting mechanical properties. The aim of the present study was to investigate Inconel 939 processed by selective laser melting (SLM) and to reveal the differences to the conventional cast alloy. Thorough examinations were conducted using electron backscatter diffraction, transmission electron microscopy, optical microscopy and mechanical testing. It is demonstrated that the microstructure of the SLM-material is highly influenced by the heat flux during layer-wise manufacturing and consequently anisotropic microstructural features prevail. An epitaxial grain growth accounts for strong bonding between the single layers resulting in good mechanical properties already in the as-built condition. A heat treatment following SLM leads to microstructural features different to those obtained after the same heat treatment of the cast alloy. Still, the mechanical performance of the latter is met underlining the potential of this technique for producing complex parts for high temperature applications.

Induced Representations of Locally Compact Groups

Abstract: 1. Basics 2. Induced representations 3. The imprimitivity theorem 4. Mackey analysis 5. Topologies on dual spaces 6. Topological Frobenius properties 7. Further applications References Index.

An optimized photon pair source for quantum circuits

Abstract: We implement an ultrafast pulsed type-II parametric down conversion source in a periodically poled KTP waveguide at telecommunication wavelengths with almost identical properties between signal and idler. As such, our source resembles closely a pure, genuine single mode photon pair source with indistinguishable modes. We measure the joint spectral intensity distribution and second order correlation functions of the marginal beams and find with both methods very low effective mode numbers corresponding to a Schmidt number below 1.16. We further demonstrate the indistinguishability as well as the purity of signal and idler photons by Hong-Ou-Mandel interferences between signal and idler and between signal/idler and a coherent field, respectively. Without using narrowband spectral filtering, we achieve a visibility for the interference between signal and idler of 94.8% and determine a purity of more than 80% for the heralded single photon states. Moreover, we measure raw heralding efficiencies of 20.5% and 15.5% for the signal and idler beams corresponding to detector-loss corrected values of 80% and 70%.

Growing Existing Customers' Revenue Streams Through Customer Referral Programs

Abstract: Customer referral programs are an effective means of customer acquisition. By assessing a large-scale customer data set from a global cellular telecommunications provider, the authors show that participation in a referral program also increases existing customers' loyalty. In a field experiment, recommenders' defection rates fell from 19% to 7% within a year, and their average monthly revenue grew by 11.4% compared with a matched control group. A negative interaction between referral program participation and customer tenure reveals that the loyalty effect of voicing a recommendation is particularly pronounced for newer customer–firm relationships. A laboratory experiment further demonstrates that referral programs with larger rewards strengthen attitudinal and behavioral loyalty, whereas smaller rewards affect only the behavioral dimension. This article contributes to our theoretical understanding of the roles played by the commitment–consistency principle and positive reinforcement theory as mechanisms ...

Causality between terrorism and economic growth

Abstract: This article analyzes the causal relationship between terrorism and economic growth, running a series of tests for Granger non–causality with panel data for a maximum of 160 countries from 1970 to ...

NetInf: An Information-Centric Design for the Future Internet

Abstract: The current Internet architecture has been very successful and has scaled well beyond the original aspirations. Nevertheless, the architecture suffers from multiple well docu- mented problems, many of which result from the fact that the usage of the Internet has changed drastically. For example, the original Internet architecture is designed to provide access to specific nodes in the network whereas today's usage is dominated by information dissemination where the information requester does not care about the source location. To adjust to those chan- ges, we develop a new, information-centric network architecture called Network of Information (NetInf ) in the context of the FP7 EU-funded 4WARD project. This architecture can significantly improve large scale information distribution. Furthermore, it supports future mobile networks in situations with intermittent and heterogeneous connectivity and connects the digital with the physical world to enable better user experience. NetInf is built upon an extended identifier/locator split which is based on a simple but powerful information model. Main aspects of NetInf include the persistent naming of information, a world- wide scalable name resolution mechanism for flat identifiers, and improved information availability and dissemination via caching and storage integrated into the network architecture.

Towards Practical Runtime Verification and Validation of Self-Adaptive Software Systems

Abstract: Software validation and verification (VV and (ii) present a proposal for including V&V operations explicitly in feedback loops for ensuring the achievement of software self-adaptation goals. Both of these contributions provide valuable starting points for V&V researchers to help advance this field.

Convergence of a cancer invasion model to a logistic chemotaxis model

Abstract: A characteristic feature of tumor invasion is the destruction of the healthy tissue surrounding it. Open space is generated, which invasive tumor cells can move into. One such mechanism is the urokinase plasminogen system (uPS), which is found in many processes of tissue reorganization. Lolas, Chaplain and collaborators have developed a series of mathematical models for the uPS and tumor invasion. These models are based upon degradation of the extracellular material through plasmid plus chemotaxis and haptotaxis. In this paper we consider the uPS invasion models in one-space dimension and we identify a condition under which this cancer invasion model converges to a chemotaxis model with logistic growth. This condition assumes that the density of the extracellular material is not too large. Our result shows that the complicated spatio-temporal patterns, which were observed by Lolas and Chaplain et al. are organized by the chaotic attractor of the logistic chemotaxis system. Our methods are based on energy estimates, where, for convergence, we needed to find lower estimates in Lγ for 0 < γ < 1. This is a new method for these types of PDE.

The Returns to Scarce Talent: Footedness and Player Remuneration in European Soccer

Abstract: The authors investigate the salary returns to the ability to play football (soccer) with both feet. The majority of footballers are predominantly right footed. Using two data sets, a cross section of footballers in the five main European leagues and a panel of players in the German Bundesliga, the authors find robust evidence of a substantial salary premium for two-footed ability, even after controlling for available player performance measures. The authors assess how this premium varies across the salary distribution and by player position.