Pushing the Limits of 3D Color Printing: Error Diffusion with Translucent Materials

Accurate color reproduction is important in many applications of 3D printing, from design prototypes to 3D color copies or portraits. Although full color is available via other technologies, multi-jet printers have greater potential for graphical 3D printing, in terms of reproducing complex appearance properties. However, to date these printers cannot produce full color, and doing so poses substantial technical challenges, from the shear amount of data to the translucency of the available color materials. In this paper, we propose an error diffusion halftoning approach to achieve full color with multi-jet printers, which operates on multiple isosurfaces or layers within the object. We propose a novel traversal algorithm for voxel surfaces, which allows the transfer of existing error diffusion algorithms from 2D printing. The resulting prints faithfully reproduce colors, color gradients and fine-scale details.Comment: 15 pages, 14 figures; includes supplemental figure

Offshoring Along the Production Chain

Recent contributions on offshoring often assume that firms can freely split their production process into separate steps which can be ranked according to the cost savings from producing abroad. We replace this assumption by the notion of a technologically determined sequence of production steps. In our model, cost savings from offshoring fluctuate along the production chain, and moving unfinished goods across borders causes transport costs. We show that, in such a setting, firms may refrain from offshoring even if relocating individual steps would be advantageous in terms of offshoring costs, or they may offshore (almost) the entire production chain to save transport costs. Small variations in model parameters may have a substantial impact on offshoring activities.

Compensation, Incentives and Risk-Taking in Principal-Agent Models

Two parties with distinct goals interact in a financial market: The risk-constrained principal provides some capital and employs the agent to invest and subsequently control the portfolio in his name. A performance-related wage schedule is agreed to compensate the agent for her actions. We investigate how risk can be transferred in this setup and what incentives are set by various contracts. In particular the high-water mark portfolio problem in discrete-time is solved

Persisting correlations of a central spin coupled to large spin baths

The decohering environment of a quantum bit is often described by the coupling to a large bath of spins. The quantum bit itself can be seen as a spin $S=1/2$ which is commonly called the central spin. The resulting central spin model describes an important mechanism of decoherence. We provide mathematically rigorous bounds for a persisting magnetization of the central spin in this model with and without magnetic field. In particular, we show that there is a well defined limit of infinite number of bath spins. Only if the fraction of very weakly coupled bath spins tends to 100\% does no magnetization persist.Comment: 19 pages, 15 figures, rigorous bounds for the central spin mode

Redefining A in RGBA: Towards a Standard for Graphical 3D Printing

Advances in multimaterial 3D printing have the potential to reproduce various visual appearance attributes of an object in addition to its shape. Since many existing 3D file formats encode color and translucency by RGBA textures mapped to 3D shapes, RGBA information is particularly important for practical applications. In contrast to color (encoded by RGB), which is specified by the object's reflectance, selected viewing conditions and a standard observer, translucency (encoded by A) is neither linked to any measurable physical nor perceptual quantity. Thus, reproducing translucency encoded by A is open for interpretation. In this paper, we propose a rigorous definition for A suitable for use in graphical 3D printing, which is independent of the 3D printing hardware and software, and which links both optical material properties and perceptual uniformity for human observers. By deriving our definition from the absorption and scattering coefficients of virtual homogeneous reference materials with an isotropic phase function, we achieve two important properties. First, a simple adjustment of A is possible, which preserves the translucency appearance if an object is re-scaled for printing. Second, determining the value of A for a real (potentially non-homogeneous) material, can be achieved by minimizing a distance function between light transport measurements of this material and simulated measurements of the reference materials. Such measurements can be conducted by commercial spectrophotometers used in graphic arts. Finally, we conduct visual experiments employing the method of constant stimuli, and derive from them an embedding of A into a nearly perceptually uniform scale of translucency for the reference materials.Comment: 20 pages (incl. appendices), 20 figures. Version with higher quality images: https://cloud-ext.igd.fraunhofer.de/s/pAMH67XjstaNcrF (main article) and https://cloud-ext.igd.fraunhofer.de/s/4rR5bH3FMfNsS5q (appendix). Supplemental material including code: https://cloud-ext.igd.fraunhofer.de/s/9BrZaj5Uh5d0cOU/downloa

From metastable to stable modifications-in situ Laue diffraction investigation of diffusion processes during the phase transitions of (GeTe)(n)Sb2Te3 (6 < n < 15) crystals.

Temperature dependent phase transitions of compounds (GeTe)nSb2Te3 (n = 6, 12, 15) have been investigated by in situ microfocus Laue diffraction. Diffusion processes involving cation defect ordering at B300 8C lead to different nanostructures which are correlated to changes of the thermoelectric characteristics

Ceramidreiche Makrodomänen und Leukozytentransmigration in die Leber bei Sepsis

Die Sphingolipide fungieren neben ihrer Aufgabe als inerte Strukturkomponente in Zellmembranen auch als aktive Metabolite für Zellprozesse wie Proliferation, Differenzierung, Apoptose und Inflammation. Insbesondere das Ceramid und das Schlüsselenzym Sphingomyelinase (SMase) spielen entscheidende Rollen bei generalisierten Inflammationsgeschehen (SIRS) sowie bei der Sepsis. Ceramidreiche Makrodomänen in Zellmembranen vermitteln eine Vielzahl von Signalkaskaden, so auch zwischen immunkompetenten Zellen, welche die inflammatorischen Abläufe bestimmen. Die Einwanderung von Leukozyten in entzündliches Gewebe, allen voran neutrophile Granulozyten, ist ein kritischer Schritt der Immunantwort des Organismus (SIRS) gegen einen eingedrungenen Erreger und kann bei Dysregulation zum Multiorganversagen führen (MOF). Die Leukozytentransmigration in das Parenchym der Organe umfasst viele Mediatoren und Signalkaskaden zwischen Neutrophilen, Endothel- und Parenchymzellen. Welche Rolle die SMase bei diesem Prozess spielt, ist bisher nicht bekannt. Vor diesem Hintergrund sollte die Frage bearbeitet werden, in welchem Maße die SMase bzw. das Ceramid die Transmigration von neutrophilen Granulozyten in die Leber beeinflusst. Darüber hinaus sollte geklärt werden, ob die SMase Einfluss auf die leukozytäre und hepatozytäre Expression von Genen für Transmigration und Chemotaxis relevante Proteine im Rahmen einer polymikrobiellen Infektion nimmt. Zur Simulation einer polymikrobiell-induzierten systemischen Inflammation wurden Wildtyp- sowie SMase-defiziente Mäuse nach dem PCI-Modell einer intraperitonealen Faecesinjektion unterzogen. Sechs Stunden post iniectionem wurden die Lebern entnommen und histologisch aufgearbeitet. Nach Esterasefärbung wurden die transmigrierten, intraparenchymalen neutrophilen Granulozyten unter dem Mikroskop quantitativ ausgewertet. Die Analyse der Genexpression wurde mittels quantitativer Real-Time-PCR von muriner Leber- sowie leukozytärer cDNA durchgeführt. Die histologische Auswertung zeigte sechs Stunden nach PCI eine verstärkte Leukozytentransmigration in die Leber der Wildtyptiere verglichen mit den SMase-depletierten Tieren. Folglich ist zu vermuten, dass durch die SMase generiertes Ceramid durch die Bildung von ceramidreichen Membrandomänen die biophysikalischen Membraneigenschaften so modifiziert, dass Signaltransduktionsvorgänge, welche die Transmigration vermitteln, amplifiziert werden. Außerdem scheint eine Ceramid-vermittelte Schädigung der Endothel- und Parenchymzellen einen chemotaktischen Gradienten zu erzeugen. Die Betrachtung der leukozytären Genexpression ergab signifikante Unterschiede zwischen Wildtyp- und SMase-defizienten Organismen. Hierbei nimmt die SMase Einfluss auf verschiedene Gene für Proteine der Leukozyten-Endothelzell-Adhäsion, Chemotaxis, Phagozytose und Transkription. Darüber hinaus schien die SMase-Defizienz eine erhöhte Bakterienlast in der Leber sowie eine verstärkte Bakteriämie zu bewirken

Temperature dependent resonant X-ray diffraction of single-crystalline Ge2Sb2Te5

The element distribution in the crystal structure of the stable phase of the well-known phase-change material Ge2Sb2Te5 was determined at temperatures up to 471 degrees C using single crystals synthesized by chemical transport reactions. Because of the similar electron count of Sb and Te, the scattering contrast was enhanced by resonant diffraction using synchrotron radiation (beamline ID11, ESRF). A simultaneous refinement on data measured at the K-absorption edges of Sb and Te as well as at additional wavelengths off the absorption edges yielded reliable occupancy factors of each element on each position (a = 4.2257(2) angstrom, c = 17.2809(18) angstrom, P (3) over bar m1, R-1 (overall) = 0.037). The dispersion correction terms Delta f' were refined and match experimental ones obtained from fluorescence spectra by the Kramers-Kronig transform. The structure contains distorted rocksalt-type blocks of nine alternating cation and anion layers, respectively, which are separated by van der Waals gaps between Te atom layers. Ge atoms prefer the cation positions near the center of the rocksalt-type block (occupancy factors Ge0.60(4)Sb0.36(2)), Sb atoms the one near the van der Waals gap (Ge0.33(7)Sb0.66(4)). Anti-site disorder is not significant. During heating up to 471 degrees C and subsequent cooling, a reversible structural distortion was observed. The refinements show that with increasing temperature the first pair of anion and cation layers next to the van der Waals gap becomes slightly detached from the block and increasingly resembles a GeTe-type layer. Thus, the difference between interatomic distances in the 3 + 3 cation coordination sphere of the mixed Ge-Sb position next to the gap becomes more pronounced. The element distribution, in contrast, neither changes during the heating experiment nor upon long-time annealing. Thus, the behavior of 9P-Ge2Sb2Te5 single crystals is predominantly under thermodynamic control