Two-Level Rectilinear Steiner Trees

Given a set $P$ of terminals in the plane and a partition of $P$ into $k$ subsets $P_1, ..., P_k$, a two-level rectilinear Steiner tree consists of a rectilinear Steiner tree $T_i$ connecting the terminals in each set $P_i$ ($i=1,...,k$) and a top-level tree $T_{top}$ connecting the trees $T_1, ..., T_k$. The goal is to minimize the total length of all trees. This problem arises naturally in the design of low-power physical implementations of parity functions on a computer chip. For bounded $k$ we present a polynomial time approximation scheme (PTAS) that is based on Arora's PTAS for rectilinear Steiner trees after lifting each partition into an extra dimension. For the general case we propose an algorithm that predetermines a connection point for each $T_i$ and $T_{top}$ ($i=1,...,k$). Then, we apply any approximation algorithm for minimum rectilinear Steiner trees in the plane to compute each $T_i$ and $T_{top}$ independently. This gives us a $2.37$-factor approximation with a running time of $\mathcal{O}(|P|\log|P|)$ suitable for fast practical computations. The approximation factor reduces to $1.63$ by applying Arora's approximation scheme in the plane

Digital långtidsbevaring i sjukvården

När datorstödda informationssystem avvecklas behöver den information som systemen innehåller i vissa fall långtidsbevaras (arkiveras). Detta kan bero på att informationen måste sparas på grund av lagstiftning eller för att den har ett historiskt värde. Denna uppsats behandlar digital långtidsbevaring utifrån OAIS-modellen, som är en generell och tekniskt obunden standard för digital långtidsbevaring. Syftet var att undersöka OAIS-modellens generalitet och om modellen bör användas som mall vid projekt för digital långtidsbevaring. Genom att undersöka två projekt där OAIS-modellen inte använts försökte jag analysera till vilken grad OAIS-modellen ändå följts. På detta sätt skulle jag kunna påvisa modellens generalitet. Den första slutsatsen jag kom fram till var att OAIS-modellens yttre flöden och inre processer är så generella att de passar in på de flesta projekt för digital långtidsbevaring, medan när modellen blir mer komplex och specifik och är den svårare att använda som mall. Den andra slutsatsen är att om OAIS-modellen skall användas som mall för mindre projekt för digital långtidsarkivering bör en mindre omfattande version utarbetas, eftersom just mer komplexa delarna som i detalj beskriver tjänster och funktioner kan te sig för specifik för det ändamål OAIS-standarden skapades för, nämligen långtidsbevaring inom rymdforskning

Interchannel coupling effects in the spin polarization of energetic photoelectrons

Effects of the interchannel coupling on the spin polarization of energetic photoelectrons emitted from atomic Ne valence subshells are examined. Like previously obtained results for cross sections and angular distributions, the photoelectron spin polarization parameters too are found considerably influenced by the coupling. The result completes a series of studies to finally conclude that the independent particle description is inadequate for the {\em entire} range of photoionization dynamics over the {\em full} spectral energy domainComment: 7 pages, 5 figures, accepted in Phys. Rev.

In vivo Analyse der hepatischen Mikrozirkulation und Inflammation im NASH-Fibrose-Tumor Mausmodell

Untersucht wurden in einem Tiermodell die morphologischen, mikrovaskulären und zellulären Aspekte der nicht-alkoholischen Fettlebererkrankung. Das NASH-Fibrose-Tumor-Modell wurde erstmalig vom Stelic Institut in Japan beschrieben. C57BL6/J Mäusen wird Streptozotocin injiziert. Ferner erhalten die Tiere eine HFD. In der Studie analysierten wir die Architektur und Mikrozirkulation der Leber in den Krankheitsstadien. Sowohl die sinusoidale Perfusion als auch die Dichte nahmen signifikant ab. Der apoptotische Zelltod sowie die Anzahl der adhärierenden Leukozyten stieg im Verlauf der Krankheit an

SPHERES, J\"ulich's High-Flux Neutron Backscattering Spectrometer at FRM II

SPHERES (SPectrometer with High Energy RESolution) is a third-generation neutron backscattering spectrometer, located at the 20 MW German neutron source FRM II and operated by the Juelich Centre for Neutron Science. It offers an energy resolution (fwhm) better than 0.65 micro-eV, a dynamic range of +-31 micro-eV, and a signal-to-noise ratio of up to 1750:1.Comment: 12 pages, 7 figures, 2 tables. Supplemental material consists of 3 pages, 2 figures, 2 table

Two electron interference in angular resolved double photoionization of Mg

The signature of the target wavefunction has been observed in the symmetrized amplitude of the resonant double photoionization of Mg. This observation is based on our experimental study of angle-resolved double photoionization of Mg at the photon energy of 55.49 eV (2p → 3d resonance) under equal energy sharing conditions

Immune-Instructive Polymers Control Macrophage Phenotype and Modulate the Foreign Body Response In Vivo

© 2020 The Author(s) Implantation of medical devices can result in inflammation. A large library of polymers is screened, and a selection found to promote macrophage differentiation towards pro- or anti-inflammatory phenotypes. The bioinstructive properties of these materials are validated within a rodent model. By identifying novel materials with immune-instructive properties, the relationship between material-immune cell interactions could be investigated, and this offers exciting possibilities to design novel bioinstructive materials that can be used for numerous clinical applications including medical implants

Innate immune cell instruction using micron-scale 3D objects of varied architecture and polymer chemistry: The ChemoArchiChip

To design effective immunomodulatory implants, innate immune cell interactions at the surface of biomaterials need to be controlled and understood. The architectural design freedom of two-photon polymerization is used to produce arrays of surface-mounted, geometrically diverse 3D polymer objects. This reveals the importance of the interplay between architecture and materials chemistry in determining human macrophage fate in vitro. The ChemoArchiChip identifies key structure-function relationships and design rules from machine learning models to build a mechanistic understanding of cell attachment and polarization. Object shape, vertex/cone angle, and size are key drivers of attachment. Particular shapes are found to heavily modulate pro- or anti-inflammatory cell polarization, while triangular pyramids drastically reduce or even eliminate attachment. Caveola-dependent endocytosis is a principal mechanism by which cells respond to objects with sharp points; i.e., low vertex/cone angles. The discovery of these putative design rules points to surfaces decorated with architectures to augment implant performance

The instrument suite of the European Spallation Source

An overview is provided of the 15 neutron beam instruments making up the initial instrument suite of the European Spallation Source (ESS), and being made available to the neutron user community. The ESS neutron source consists of a high-power accelerator and target station, providing a unique long-pulse time structure of slow neutrons. The design considerations behind the time structure, moderator geometry and instrument layout are presented. The 15-instrument suite consists of two small-angle instruments, two reflectometers, an imaging beamline, two single-crystal diffractometers; one for macromolecular crystallography and one for magnetism, two powder diffractometers, and an engineering diffractometer, as well as an array of five inelastic instruments comprising two chopper spectrometers, an inverse-geometry single-crystal excitations spectrometer, an instrument for vibrational spectroscopy and a high-resolution backscattering spectrometer. The conceptual design, performance and scientific drivers of each of these instruments are described. All of the instruments are designed to provide breakthrough new scientific capability, not currently available at existing facilities, building on the inherent strengths of the ESS long-pulse neutron source of high flux, flexible resolution and large bandwidth. Each of them is predicted to provide world-leading performance at an accelerator power of 2 MW. This technical capability translates into a very broad range of scientific capabilities. The composition of the instrument suite has been chosen to maximise the breadth and depth of the scientific impact o