Showing papers by "University of Paderborn published in 2015"
TL;DR: The design of the hologram integrates a ground metal plane with a geometric metasurface that enhances the conversion efficiency between the two circular polarization states, leading to high diffraction efficiency without complicating the fabrication process.
Abstract: Using a metasurface comprising an array of nanorods with different orientations and a backreflector, a hologram image can be obtained in the visible and near-infrared with limited loss of light intensity.
2,075 citations
TL;DR: In this article, a survey and critical analysis focused on a variety of chemotaxis models in biology, namely the classical Keller-Segel model and its subsequent modifications, which, in several cases, have been developed to obtain models that prevent the non-physical blow up of solutions.
Abstract: This paper proposes a survey and critical analysis focused on a variety of chemotaxis models in biology, namely the classical Keller–Segel model and its subsequent modifications, which, in several cases, have been developed to obtain models that prevent the non-physical blow up of solutions. The presentation is organized in three parts. The first part focuses on a survey of some sample models, namely the original model and some of its developments, such as flux limited models, or models derived according to similar concepts. The second part is devoted to the qualitative analysis of analytic problems, such as the existence of solutions, blow-up and asymptotic behavior. The third part deals with the derivation of macroscopic models from the underlying description, delivered by means of kinetic theory methods. This approach leads to the derivation of classical models as well as that of new models, which might deserve attention as far as the related analytic problems are concerned. Finally, an overview of the entire contents leads to suggestions for future research activities.
861 citations
TL;DR: The analytic network process (ANP) is used to deal with the interdependencies among the criteria, and the traditional Grey relational analysis (GRA) has been modified to better address the uncertainties inherent in supplier selection decisions.
430 citations
TL;DR: The continuous phase engineering of the effective nonlinear polarizability enables complete control over the propagation of harmonic generation signals, paving the way for highly compact nonlinear nanophotonic devices.
Abstract: The capability of locally engineering the nonlinear optical properties of media is crucial in nonlinear optics. Although poling is the most widely employed technique for achieving locally controlled nonlinearity, it leads only to a binary nonlinear state, which is equivalent to a discrete phase change of π in the nonlinear polarizability. Here, inspired by the concept of spin-rotation coupling, we experimentally demonstrate nonlinear metasurfaces with homogeneous linear optical properties but spatially varying effective nonlinear polarizability with continuously controllable phase. The continuous phase control over the local nonlinearity is demonstrated for second and third harmonic generation by using nonlinear metasurfaces consisting of nanoantennas of C3 and C4 rotational symmetries, respectively. The continuous phase engineering of the effective nonlinear polarizability enables complete control over the propagation of harmonic generation signals. Therefore, this method seamlessly combines the generation and manipulation of harmonic waves, paving the way for highly compact nonlinear nanophotonic devices.
371 citations
TL;DR: The paper summarizes the discussion on smart services, adds an extensive literature review, provides examples from business practice and develops a structured approach to new research avenues.
Abstract: Purpose – The purpose of this paper is to craft a future research agenda to advance smart service research and practice. Smart services are delivered to or via intelligent objects that feature awareness and connectivity. For service researchers and managers, one of the most fascinating aspects of smart service provision is that the connected object is able to sense its own condition and its surroundings and thus allows for real-time data collection, continuous communication and interactive feedback. Design/methodology/approach – This article is based on discussions in the workshop on “Fresh perspectives on technology in service” at the International Network of Service Researchers on September 26, 2014 at CTF, Karlstad, Sweden. The paper summarizes the discussion on smart services, adds an extensive literature review, provides examples from business practice and develops a structured approach to new research avenues. Findings – We propose that smart services vary on their individual level of autonomous dec...
281 citations
TL;DR: Transform-limited linewidths measured on second timescales are reported, primarily on the neutral exciton but also on the charged exciton close to saturation.
Abstract: Developing a quantum photonics network requires a source of very-high-fidelity single photons. An outstanding challenge is to produce a transform-limited single-photon emitter to guarantee that single photons emitted far apart in the time domain are truly indistinguishable. This is particularly difficult in the solid-state as the complex environment is the source of noise over a wide bandwidth. A quantum dot is a robust, fast, bright and narrow-linewidth emitter of single photons; layer-by-layer growth and subsequent nano-fabrication allow the electronic and photonic states to be engineered. This represents a set of features not shared by any other emitter but transform-limited linewidths have been elusive. Here, we report transform-limited linewidths measured on second timescales, primarily on the neutral exciton but also on the charged exciton close to saturation. The key feature is control of the nuclear spins, which dominate the exciton dephasing via the Overhauser field.
230 citations
TL;DR: The German, Austrian and Swiss nutrition societies are the joint editors of the 'reference values for nutrient intake' and revised the reference values for the intake of selenium and published them in February 2015.
223 citations
TL;DR: In this paper, the existence of global weak solutions to the chemotaxis system u t = Δ u − ∇ ⋅ ( u ∇ v ) + κ u − μ u 2 v t, under homogeneous Neumann boundary conditions in a smooth bounded convex domain Ω ⊂ R n, for arbitrarily small values of μ > 0.
211 citations
TL;DR: It is shown that the three main requirements to construct a valid framework for QIS -- the controlled generation of resource states, the targeted and highly efficient manipulation of temporal modes and their efficient detection -- can be fulfilled with current technology.
Abstract: Because photons interact weakly with themselves and experience low decoherence, they are a promising avenue for quantum information science. Theorists show how the temporal modes of single-photon states can form an alphabet for communication across a quantum information network.
210 citations
TL;DR: In this paper, a priori estimation method was proposed to obtain global boundedness and asymptotics of large-data solutions in a three-dimensional chemotaxis-fluid system of type (0.1).
Abstract: We consider the chemotaxis-fluid system 0.1
in a bounded convex domain $$\Omega \subset {\mathbb {R}}^3$$
with smooth boundary, where $$\phi \in W^{1,\infty }(\Omega )$$
and D, f and S are given functions with values in $$[0,\infty ), [0,\infty )$$
and $${\mathbb {R}}^{3\times 3}$$
, respectively. In the existing literature, the derivation of results on global existence and qualitative behavior essentially relies on the use of energy-type functionals which seem to be available only in special situations, necessarily requiring the matrix-valued S to actually reduce to a scalar function of c which, along with f, in addition should satisfy certain quite restrictive structural conditions. The present work presents a novel a priori estimation method which allows for removing any such additional hypothesis: besides appropriate smoothness assumptions, in this paper it is only required that f is locally bounded in $$[0,\infty )$$
, that S is bounded in $$\Omega \times [0,\infty )^2$$
, and that $$D(n)\ge k_{D}n^{m-1}$$
for all $$n\ge 0$$
with some $$k_{D}>0$$
and some $$\begin{aligned} m>\frac{7}{6}. \end{aligned}$$
It is shown that then for all reasonably regular initial data, a corresponding initial-boundary value problem for (0.1) possesses a globally defined weak solution. The method introduced here is efficient enough to moreover provide global boundedness of all solutions thereby obtained in that, inter alia, $$n\in L^\infty (\Omega \times (0,\infty ))$$
. Building on this boundedness property, it can finally even be proved that in the large time limit, any such solution approaches the spatially homogeneous equilibrium $$(\overline{n_0},0,0)$$
in an appropriate sense, where $$\overline{n_0}:=\frac{1}{|\Omega |} \int _{\Omega }n_0$$
, provided that merely $$n_0
ot \equiv 0$$
and $$f>0$$
on $$(0,\infty )$$
. To the best of our knowledge, these are the first results on boundedness and asymptotics of large-data solutions in a three-dimensional chemotaxis-fluid system of type (0.1).
200 citations
TL;DR: In this paper, a coupled chemotaxis-fluid system is considered under no-flux boundary conditions for n and c and no-slip boundary condition for u in three-dimensional bounded domains with smooth boundary, and it is shown that the corresponding initial-boundary problem possesses a global classical solution which is bounded.
Abstract: The coupled chemotaxis–fluid system
$$\left\{ \begin{array}{lll} &n_t + u\cdot
abla n = \Delta n -
abla \cdot (n
abla c) +rn-\mu n^2, \\ & c_t + u\cdot
abla c = \Delta c-c+n , \\ & u_t +
abla P = \Delta u + n
abla \phi + g(x,t), \\ &
abla \cdot u = 0, \end{array}\right.$$
is considered under no-flux boundary conditions for n and c and no-slip boundary conditions for u in three-dimensional bounded domains with smooth boundary, where $${r\geq 0}$$
and $${\mu > 0}$$
are given constants and $${\phi\in W^{1, \infty}(\Omega)}$$
and $${g\in C^1(\bar\Omega\times [0, \infty)) \cap L^\infty(\Omega\times (0,\infty))}$$
are prescribed parameter functions. It is shown that under the explicit condition $${\mu\geq 23}$$
and suitable regularity assumptions on the initial data, the corresponding initial-boundary problem possesses a global classical solution which is bounded. Apart from this, it is proved that if r = 0, then both n(·, t) and c(·, t) decay to zero with respect to the norm in $${L^\infty(\Omega)}$$
as $${t\to \infty}$$
, and that if, moreover, $${\int_0^\infty \int_\Omega |g|^2 < \infty}$$
, then also u(·, t)→ 0 in $${L^\infty(\Omega)}$$
as $${t\to \infty}$$
.
TL;DR: The authors disentangles the effect of prior entrepreneurial exposure on entrepreneurial intention in terms of different types of exposure and their perceived quality, and analyzes whether attitude, subjective norm, and perceived behavioral control mediate the influence of entrepreneurial role models and work experience in small or newly founded firms.
TL;DR: An effective way for broadband holographic multiplexing based on geometric metasurfaces is demonstrated by the integration of several recording channels into a single device, paving the way for a wide range of applications related to optical patterning, encryption, and information processing.
Abstract: An effective way for broadband holographic multiplexing based on geometric metasurfaces is demonstrated by the integration of several recording channels into a single device. Each image can be individually addressed with a unique set of parameters, such as circular polarization, position, and angle. Such a technique paves the way for a wide range of applications related to optical patterning, encryption, and information processing.
TL;DR: In this paper, the authors synthesize prior literature regarding the CE-performance relationship of 43 independent samples including 13,237 firms and find that strategic renewal, innovation and corporate venturing positively influence overall, subjective and objective firm performance.
Abstract: Despite considerable research, empirical findings on the relationship between corporate entrepreneurship (CE) (i.e., strategic renewal, innovation and corporate venturing) and performance remain inconclusive. Using a meta-analysis, the present paper synthesizes prior literature regarding the CE–performance relationship of 43 independent samples including 13,237 firms. Our results reveal that strategic renewal, innovation and corporate venturing positively influence overall, subjective and objective firm performance. In addition, we conduct moderator analyses to reflect on the context and to verify whether and how the relationships vary in the presence of several study-specific factors. We find that innovation has a stronger effect on performance in high-tech as opposed to low-tech industries, and the association between corporate venturing and performance is the strongest in Europe (compared with North America and Asia). Against our theoretical predictions, we find the association between strategic renewal and performance to be stronger for larger than for smaller firms. Based on our results, we derive recommendations for future research and point to managerial implications.
TL;DR: In this paper, the authors examine whether the mandated introduction of International Financial Reporting Standards (IFRS) is associated with the propensity to access the public rather than private debt market and the cost of debt.
Abstract: We examine whether the mandated introduction of International Financial Reporting Standards (IFRS) is associated with the propensity to access the public rather than private debt market and the cost of debt. We use a global sample of public bonds and private loans and find that mandatory IFRS adopters are more likely, post-IFRS, to issue bonds than to borrow privately. We also find that mandatory IFRS adopters pay lower bond yield spreads, but not lower loan spreads, after the mandate. These findings are consistent with debt providers responding positively to financial reporting of higher quality and comparability, but only when there is a greater reliance on publicly available financial statements than private communication. Lastly, we document that the observed debt market benefits are concentrated in countries with larger differences between domestic GAAP and IFRS and are present even for EU countries that did not experience concurrent financial reporting enforcement or other institutional reforms. Overall, our study documents positive economic consequences around the mandated IFRS adoption for corporate debt financing and, in particular, for bond financing.
01 Dec 2015
TL;DR: A new beamformer front-end for Automatic Speech Recognition that leverages the power of a bi-directional Long Short-Term Memory network to robustly estimate soft masks for a subsequent beamforming step and achieves a 53% relative reduction of the word error rate over the best baseline enhancement system for the relevant test data set.
Abstract: We present a new beamformer front-end for Automatic Speech Recognition and apply it to the 3rd-CHiME Speech Separation and Recognition Challenge. Without any further modification of the back-end, we achieve a 53% relative reduction of the word error rate over the best baseline enhancement system for the relevant test data set. Our approach leverages the power of a bi-directional Long Short-Term Memory network to robustly estimate soft masks for a subsequent beamforming step. The utilized Generalized Eigenvalue beamforming operation with an optional Blind Analytic Normalization does not rely on a Direction-of-Arrival estimate and can cope with multi-path sound propagation, while at the same time only introducing very limited speech distortions. Our quite simple setup exploits the possibilities provided by simulated training data while still being able to generalize well to the fairly different real data. Finally, combining our front-end with data augmentation and another language model nearly yields a 64 % reduction of the word error rate on the real data test set.
TL;DR: It is demonstrated that CL and EELS are closely related to optical scattering and extinction, respectively, with the addition of nanometer spatial resolution and is traced back to plasmon dissipation.
Abstract: Plasmon modes of the exact same individual gold nanoprisms are investigated through combined nanometer-resolved electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) measurements. We show that CL only probes the radiative modes, in contrast to EELS, which additionally reveals dark modes. The combination of both techniques on the same particles thus provides complementary information and also demonstrates that although the radiative modes give rise to very similar spatial distributions when probed by EELS or CL, their resonant energies appear to be different. We trace this phenomenon back to plasmon dissipation, which affects in different ways the plasmon signatures probed by these techniques. Our experiments are in agreement with electromagnetic numerical simulations and can be further interpreted within the framework of a quasistatic analytical model. We therefore demonstrate that CL and EELS are closely related to optical scattering and extinction, respectively, with the addition of nanometer spatial resolution.
TL;DR: It is concluded that firms should not shift customers toward self-service channels completely, especially not at the beginning of a relationship, and the notion of actively managing customers' cocreation of value is stressed.
Abstract: Advancements in information technology have changed the way customers experience a service encounter and their relationship with service providers. Especially technology-based self-service channels have found their way into the 21st century service economy. While research embraces these channels for their cost-efficiency, it has not examined whether a shift from personal to self-service affects customer--firm relationships. Drawing from the service-dominant logic and its central concept of value-in-context, we discuss customers' value creation in self-service and personal service channels and examine the long-term impact of these channels on customer retention. Using longitudinal customer data, we investigate how the ratio of self-service versus personal service use influences customer defection over time. Our findings suggest that the ratio of self-service to personal service used affects customer defection in a U-shaped manner, with intermediate levels of both self-service and personal service use being associated with the lowest likelihood of defection. We also find that this effect mitigates over time. We conclude that firms should not shift customers toward self-service channels completely, especially not at the beginning of a relationship. Our study underlines the importance of understanding when and how self-service technologies create valuable customer experiences and stresses the notion of actively managing customers' cocreation of value.
TL;DR: In this paper, the authors considered a chemotaxis system under no-flux boundary conditions in a bounded domain with smooth boundary, where the density of a cell population and the concentration of an attractive chemical consumed by the cell were considered.
Abstract: The chemotaxis system $u_t=\Delta u -
abla \cdot (uS(x,u,v)\cdot
abla v);\ v_t=\Delta v - uf(v)$ (referred to as ($\star$) in this abstract), for the density $u=u(x,t)$ of a cell population and the concentration $v=v(x,t)$ of an attractive chemical consumed by the former, is considered under no-flux boundary conditions in a bounded domain $\Omega\subset{\mathbb{R}}^n$, $n\ge 1$, with smooth boundary, where $f \in C^1([0,\infty);[0,\infty))$ and $S \in C^2(\bar\Omega\times [0,\infty)^2;{\mathbb{R}}^{n\times n})$ are given functions such that f(0)=0. In contrast to related Keller--Segel-type problems with scalar sensitivities, in the presence of such matrix-valued $S$ the system ($\star$) in general apparently does not possess any useful gradient-like structure. Accordingly, its analysis needs to be based on new types of a priori bounds. Using a spatio-temporal $L^2$ estimate for $
abla \ln (u+1)$ as a starting point, we derive a series of compactness properties of solutions to suitably regularized vers...
TL;DR: In this paper, a large-scale sample of 816 salespeople and directors from 30 sales organizations, and employing multilevel structural equation modeling, was drawn to shed light on the chain of effects that transforms sales strategy as an organizational variable into selling performance captured on the individual salesperson level.
04 Jul 2015
TL;DR: Based on the coding results, information about the different fields of Computing Education at schools, the intended goals and competencies, the taught content, the applied programming languages and tools and the different forms of assessment and teacher education is summarized.
Abstract: In two special issues of the ACM journal "Transactions on Computing Education" (TOCE), 14 extensive case studies about the various situations of Computer Science Education (CSE) in K-12 schools in 12 countries (respectively states) were collected. During the work at the ITiCSE 2015, we have performed a deductive qualitative text analysis on these case studies in order to extract the most useful information. As a category system, we applied some selected categories of the Darmstadt Model that was developed by the working group "Computer Science/Informatics in Secondary Schools" at the ITiCSE 2011. Based on the coding results, we summarized information about the different fields of Computing Education at schools, the intended goals and competencies, the taught content, the applied programming languages and tools and the different forms of assessment and teacher education. Despite the limitations of the analyzed articles, representing just snapshots of complex situations from the specific viewpoint of the respective authors, we were able to collect some interesting results.
TL;DR: In this article, the authors present a methodology to help end-users to find appropriate part candidates for the use of the additive manufacturing (AM) technology, and the concept furthermore includes approaches for redesigning current available parts.
Abstract: Purpose – This paper aims to present a methodology to help end-users to find appropriate part candidates for the use of the additive manufacturing (AM) technology. These shall be capable of bringing AM into their businesses. The concept furthermore includes approaches for redesigning current available parts and helps to estimate the economic implications of the use of the technology. Design/methodology/approach – The approach starts to discuss general economic aspects for the successful use of AM. While describing the introduction of new technologies into existing businesses, the importance of an appropriate part selection for AM is pointed out. A methodology for a part selection process is presented, and the different criteria are developed. An approach for a redesign of the selected parts, including the gathering of requirements, is given based on different sample parts. A variation of criteria to include measures for product piracy is highlighted. Findings – The methodology has proven applicability in ...
TL;DR: In this article, a process-independent method for the development of Design Rules for additive manufacturing is presented. But the developed Design Rules can only apply for the considered additive manufacturing technologies.
Abstract: Purpose – The purpose of this paper is to present Design Rules for additive manufacturing and a method for their development. Design/methodology/approach – First, a process-independent method for the development of Design Rules was worked out. Therefore, geometrical standard elements and attributes that characterize the elements’ shapes have been defined. Next, the standard elements have been manufactured with different attribute values with Laser Sintering, Laser Melting and Fused Deposition Modeling, and their geometrical quality was examined. From the results, Design Rules for additive manufacturing were derived and summarized in a catalogue. Findings – Due to the process independent method, Design Rules were developed that apply for the different considered additive manufacturing technologies equally. These Design Rules are completely function-independent and easily transferable to individual part designs. Research limitations/implications – The developed Design Rules can only apply for the considered...
TL;DR: This study proposes a three-stage hybrid method for selecting an optimal combination of projects and obtains the maximum fitness between the final selection and the project initial rankings while considering various organizational objectives.
Abstract: Project portfolio selection is a complex and difficult task in fuzzy environments.A three-stage hybrid method is used to select an optimal combination of projects.Data Envelopment Analysis is used to screen the available projects.TOPSIS is used to rank the potentially promising projects.Linear Integer Programming is used to select the most suitable project portfolio. Project selection and resource allocation are critical issues in project-based organizations. These organizations are required to plan, evaluate, and control their projects in accordance with the organizational mission and objectives. In this study, we propose a three-stage hybrid method for selecting an optimal combination of projects. We obtain the maximum fitness between the final selection and the project initial rankings while considering various organizational objectives. The proposed model is comprised of three stages and each stage is composed of several steps and procedures. We use Data Envelopment Analysis (DEA) for the initial screening, the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) for ranking the projects, and linear Integer Programming (IP) for selecting the most suitable project portfolio in a fuzzy environment according to organizational objectives. Finally, a case study is used to demonstrate the applicability of the proposed method and exhibit the efficacy of the algorithms and procedures.
TL;DR: In this paper, the authors identify missing links in the literature and to craft a future research agenda to advance loyalty program research and practice, focusing on three key areas: (1) LP designs, (2) Assessment of LP performance, and (3) Emerging trends and the impact of new technologies.
Abstract: Despite the growing literature on loyalty program (LP) research, many questions remain underexplored. Driven by advancements in information technology, marketing analytics, and consumer interface platforms (e.g., mobile devices), there have been many recent developments in LP practices around the world. They impose new challenges and create exciting opportunities for future LP research. The main objective of this paper is to identify missing links in the literature and to craft a future research agenda to advance LP research and practice. Our discussion focuses on three key areas: (1) LP designs, (2) Assessment of LP performance, and (3) Emerging trends and the impact of new technologies. We highlight several gaps in the literature and outline research opportunities in each area.
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TL;DR: In this paper, the authors consider a chemotaxis-fluid system involving nonlinear cell diffusion of porous medium type, signal consumption by cells, and rather general, possibly matrix-valued, chemotactic sensitivities.
Abstract: We consider a chemotaxis-fluid system involving nonlinear cell diffusion of porous medium type, signal consumption by cells, and rather general, possibly matrix-valued, chemotactic sensitivities. It is shown that if the corresponding diffusion exponent $m$ satisfies $m>7/6$, then for all reasonably regaular initial data an associated initial-boundary value problem in smoothly bounded three-dimensional domains possesses a globally defined weak solution which is bounded. Under a mild additional assumption on the signal consumption rate, it is moreover shown that any nontrivial of these solutions stabilizes toward a spatially homogeneous equilibrium in the large time limit.
TL;DR: In this article, a resistive gas sensor for carbon monoxide (CO) in low ppm concentrations is used, and the operating temperature has a strong impact on the concentration-dependent sensing behavior.
Abstract: Cobalt oxide spinel (Co 3 O 4 ) with an ordered nanostructure is used as a resistive gas sensor for carbon monoxide (CO) in low ppm concentrations. The operating temperature has a strong impact on the concentration-dependent sensing behavior. At lower temperature (473 K) the sensor response is governed mainly by surface coverage with CO and/or CO 2 , whereas at higher temperature (563 K) oxygen diffusion in the crystal lattice of Co 3 O 4 strongly affects the sensing behavior.
TL;DR: In this article, the authors introduce the concept of relational attractiveness of the customer (RAC) which is defined as the attitude of the supplier towards the customer firm in order to maintain and/or to improve an existing business relationship.
08 Jan 2015-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the microstructure after layer-wise processing partially consists of metastable-retained austenite which transforms to martensite in a subsequent tensile test.
Abstract: Microstructural characterization of hot work tool steel processed by selective laser melting was carried out. The findings shed light on the interrelationship between processing parameters and the microstructural evolution. It was found that the microstructure after layer-wise processing partially consists of metastable-retained austenite which transforms to martensite in a subsequent tensile test. This improves the mechanical properties of the hot work tool steel enabling direct application.
TL;DR: In this paper, the pore-based fatigue strength prediction for a titanium alloy TiAl6V4 has become feasible, but the obtained accuracies are subjected to scatter, which is probably caused by the high defect density even present in SLM materials manufactured following optimized processing routes.
Abstract: Selective laser melting (SLM), as a metalworking additive manufacturing technique, received considerable attention from industry and academia due to unprecedented design freedom and overall balanced material properties. However, the fatigue behavior of SLM-processed materials often suffers from local imperfections such as micron-sized pores. In order to enable robust designs of SLM components used in an industrial environment, further research regarding process-induced porosity and its impact on the fatigue behavior is required. Hence, this study aims at a transfer of fatigue prediction models, established for conventional process-routes, to the field of SLM materials. By using high-resolution computed tomography, load increase tests, and electron microscopy, it is shown that pore-based fatigue strength predictions for a titanium alloy TiAl6V4 have become feasible. However, the obtained accuracies are subjected to scatter, which is probably caused by the high defect density even present in SLM materials manufactured following optimized processing routes. Based on thorough examination of crack surfaces and crack initiation sites, respectively, implications for optimization of prediction accuracy of the models in focus are deduced.