University of Paderborn

About: University of Paderborn is a education organization based out in Paderborn, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Computer science & Context (language use). The organization has 6684 authors who have published 16929 publications receiving 323154 citations.

A carpet cloak for visible light.

Abstract: We report an invisibility carpet cloak device, which is capable of making an object undetectable by visible light. The cloak is designed using quasi conformal mapping and is fabricated in a silicon nitride waveguide on a specially developed nanoporous silicon oxide substrate with a very low refractive index (n<1.25). The spatial index variation is realized by etching holes of various sizes in the nitride layer at deep subwavelength scale creating a local effective medium index. The fabricated device demonstrates wideband invisibility throughout the visible spectrum with low loss. This silicon nitride on low index substrate can also be a general scheme for implementation of transformation optical devices at visible frequencies.

Entrepreneurship and Structural Economic Transformation

Abstract: This paper provides an endogenous growth model to illuminate the role of entrepreneurial start-up firms in structural economic transformation. We follow the Lewis-model distinction between a traditional and modern sector and underpin this distinction with micro-foundations. We specify mature and start-up entrepreneurs and make a distinction between survivalist self-employment activities in the traditional sector and opportunity-driven entrepreneurship in the modern. The model shows how opportunity-driven entrepreneurship can drive structural transformation in both the modern and traditional sectors through innovation and the provision of intermediate inputs and services (which permits greater specialization in manufacturing) and by increasing employment and productivity.

The Weak and Strong Lefschetz Properties for Artinian K-Algebras

Abstract: Let A = bigoplus_{i >= 0} A_i be a standard graded Artinian K-algebra, where char K = 0. Then A has the Weak Lefschetz property if there is an element ell of degree 1 such that the multiplication times ell : A_i --> A_{i+1} has maximal rank, for every i, and A has the Strong Lefschetz property if times ell^d : A_i --> A_{i+d} has maximal rank for every i and d. The main results obtained in this paper are the following. 1) EVERY height three complete intersection has the Weak Lefschetz property. (Our method, surprisingly, uses rank two vector bundles on P^2 and the Grauert-Mulich theorem.) 2) We give a complete characterization (including a concrete construction) of the Hilbert functions that can occur for K-algebras with the Weak or Strong Lefschetz property (and the characterization is the same one). 3) We give a sharp bound on the graded Betti numbers (achieved by our construction) of Artinian K-algebras with the Weak or Strong Lefschetz property and fixed Hilbert function. This bound is again the same for both properties. Some Hilbert functions in fact FORCE the algebra to have the maximal Betti numbers. 4) EVERY Artinian ideal in K[x,y] possesses the Strong Lefschetz property. This is false in higher codimension.

Nonlinear optics at all-dielectric nanoantennas and metasurfaces

Abstract: Freed from phase-matching constraints, plasmonic metasurfaces have contributed significantly to the control of the optical nonlinearity and enhancing the nonlinear generation efficiency by engineering subwavelength meta-atoms. However, the high dissipative losses and the inevitable thermal heating limit their applicability in nonlinear nanophotonics. All-dielectric metasurfaces, supporting both electric and magnetic Mie-type resonances in their nanostructures, have appeared as a promising alternative to nonlinear plasmonics. High-index dielectric nanostructures, allowing additional magnetic resonances, can induce magnetic nonlinear effects, which along with electric nonlinearities increase the nonlinear conversion efficiency. In addition, low dissipative losses and high damage thresholds provide an extra degree of freedom for operating at high pump intensities, resulting in a considerable enhancement of the nonlinear processes. In this review, we discuss the current state-of-the-art in the intensely developing area of all-dielectric nonlinear nanostructures and metasurfaces, including the role of Mie modes, Fano resonances and anapole moments for harmonic generation, wave mixing, and ultrafast optical switching. Furthermore, we review the recent progress in the nonlinear phase and wavefront control using all-dielectric metasurfaces. We discuss techniques to realize all-dielectric metasurfaces for multifunctional applications and generation of second-order nonlinear processes from CMOS compatible materials.

Integrating UML diagrams for production control systems

Abstract: The paper proposes to use SDL block diagrams, UML class diagrams, and UML behavior diagrams like collaboration diagrams, activity diagrams, and statecharts as a visual programming language. We describe a modeling approach for flexible, autonomous production agents, which are used for the decentralization of production control systems. In order to generate a (Java) implementation of a production control system from its specification, we define a precise semantics for the diagrams and we define how different (kinds of) diagrams are combined to a complete executable specification. Generally, generating code from UML behavior diagrams is not well understood. Frequently, the semantics of a UML behavior diagram depends on the topic and the aspect that is modeled and on the designer that created it. In addition, UML behavior diagrams usually model only example scenarios and do not describe all possible cases and possible exceptions. We overcome these problems by restricting the UML notation to a subset of the language that has a precise semantics. In addition, we define which kind of diagram should be used for which purpose and how the different kinds of diagrams are integrated to a consistent overall view.