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: Control reconfiguration & Software. The organization has 6684 authors who have published 16929 publications receiving 323154 citations.

On design for additive manufacturing: evaluating geometrical limitations

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...

The supersingular locus of the Shimura variety of GU(1 ,n − 1) II

Abstract: We complete the study of the supersingular locus $\mathcal{M}^{\mathrm{ss}}$ in the fiber at p of a Shimura variety attached to a unitary similitude group GU(1,n−1) over ℚ in the case that p is inert. This was started by the first author in Can. J. Math. 62, 668–720 (2010) where complete results were obtained for n=2,3. The supersingular locus $\mathcal{M}^{\mathrm{ss}}$ is uniformized by a formal scheme $\mathcal{N}$ which is a moduli space of so-called unitary p-divisible groups. It depends on the choice of a unitary isocrystal N. We define a stratification of $\mathcal{N}$ indexed by vertices of the Bruhat-Tits building attached to the reductive group of automorphisms of N. We show that the combinatorial behavior of this stratification is given by the simplicial structure of the building. The closures of the strata (and in particular the irreducible components of $\mathcal{N}_{\mathrm{red}}$ ) are identified with (generalized) Deligne-Lusztig varieties. We show that the Bruhat-Tits stratification is a refinement of the Ekedahl-Oort stratification and also relate the Ekedahl-Oort strata to Deligne-Lusztig varieties. We deduce that $\mathcal{M}^{\mathrm{ss}}$ is locally a complete intersection, that its irreducible components and each Ekedahl-Oort stratum in every irreducible component is isomorphic to a Deligne-Lusztig variety, and give formulas for the number of irreducible components of every Ekedahl-Oort stratum of $\mathcal{M}^{\mathrm{ss}}$ .

Finite-time blow-up in the higher-dimensional parabolic-parabolic Keller-Segel system

Abstract: We study the Neumann initial-boundary value problem for the fully parabolic Keller-Segel system u_t=\Delta u - abla \cdot (u abla v), \qquad x\in\Omega, \ t>0, [1mm] v_t=\Delta v-v+u, \qquad x\in\Omega, \ t>0, where $\Omega$ is a ball in ${\mathbb{R}}^n$ with $n\ge 3$. It is proved that for any prescribed $m>0$ there exist radially symmetric positive initial data $(u_0,v_0) \in C^0(\bar\Omega) \times W^{1,\infty}(\Omega)$ with $\int_\Omega u_0=m$ such that the corresponding solution blows up in finite time. Moreover, by providing an essentially explicit blow-up criterion it is shown that within the space of all radial functions, the set of such blow-up enforcing initial data indeed is large in an appropriate sense; in particular, this set is dense with respect to the topology of $L^p(\Omega) \times W^{1,2}(\Omega)$ for any $p \in (1,\frac{2n}{n+2})$.

Theoretical study of the mechanism of dry oxidation of 4H-SiC

Abstract: Possible defect structures, arising from the interaction of ${\mathrm{O}}_{2}$ molecules with an ideal portion of the $\mathrm{SiC}∕\mathrm{Si}{\mathrm{O}}_{2}$ interface, have been investigated systematically using density functional theory. Based on the calculated total energies and assuming thermal quasiequilibrium during oxidation, the most likely routes leading to complete oxidation have been determined. The defect structures produced along these routes will remain at the interface in significant concentration when stopping the oxidation process. The results obtained for their properties are well supported by experimental findings about the $\mathrm{SiC}∕\mathrm{Si}{\mathrm{O}}_{2}$ interface. It is found that carbon-carbon bonds can explain most of the observed interface states but not the high density near the conduction band of $4H$-SiC.

HERFD-XAS and valence-to-core-XES: new tools to push the limits in research with hard X-rays?

Abstract: In this perspective, the HERFD-XANES (high energy resolution fluorescence detected X-ray absorption near edge structure) and Kβ2,5- or V2C-XES (valence-to-core X-ray emission spectroscopy) methods are discussed as new and powerful tools for chemical research with hard X-rays. This includes a brief survey of the underlying physical processes and the introduction of experimental issues. The potential of both methods to overcome limitations of conventional XAS (X-ray absorption spectroscopy) and to push the limits for obtaining new information about the electronic and geometric structures of metal centers, in the solid state structure or heterogeneous catalysts, but also in metal complexes and homogeneous catalysts, is discussed by presenting a survey of representative references and recent own studies, rounded off by a conclusion and outlook.