On the monodromy of the Hitchin connection

For any genus g > 1 we give an example of a family of smooth complex projective curves of genus g such that the image of the monodromy representation of the Hitchin connection on the sheaf of generalized SL(2)-theta functions of level l different from 1,2,4 and 8 contains an element of infinite order.Comment: 20 pages, revised versio

Deterministic coupling of a single silicon-vacancy color center to a photonic crystal cavity in diamond

Deterministic coupling of single solid-state emitters to nanocavities is the key for integrated quantum information devices. We here fabricate a photonic crystal cavity around a preselected single silicon-vacancy color center in diamond and demonstrate modification of the emitters internal population dynamics and radiative quantum efficiency. The controlled, room-temperature cavity coupling gives rise to a resonant Purcell enhancement of the zero-phonon transition by a factor of 19, coming along with a 2.5-fold reduction of the emitter's lifetime

The Metalloprotease Meprin β Is an Alternative β-Secretase of APP

The membrane bound metalloprotease meprin β is important for collagen fibril assembly in connective tissue formation and for the detachment of the intestinal mucus layer for proper barrier function. Recent proteomic studies revealed dozens of putative new substrates of meprin β, including the amyloid precursor protein (APP). It was shown that APP is cleaved by meprin β in distinct ways, either at the β-secretase site resulting in increased levels of Aβ peptides, or at the N-terminus releasing 11 kDa, and 20 kDa peptide fragments. The latter event was discussed to be rather neuroprotective, whereas the ectodomain shedding of APP by meprin β reminiscent to BACE-1 is in line with the amyloid hypothesis of Alzheimer's disease, promoting neurodegeneration. The N-terminal 11 kDa and 20 kDa peptide fragments represent physiological cleavage products, since they are found in human brains under different diseased or non-diseased states, whereas these fragments are completely missing in brains of meprin β knock-out animals. Meprin β is not only a sheddase of adhesion molecules, such as APP, but was additionally demonstrated to cleave within the prodomain of ADAM10. Activated ADAM10, the α-secretase of APP, is then able to shed meprin β from the cell surface thereby abolishing the β-secretase activity. All together meprin β seems to be a novel player in APP processing events, even influencing other enzymes involved in APP cleavage

Objective homogeneity quantification of a periodic surface using the Gini coefficient

The significance of periodic surface structuring methods, such as direct laser interference patterning, is growing steadily. Thus, the ability to objectively and consistently evaluate these surfaces is increasingly important. Standard parameters such as surface roughness or the arithmetic average height are meant to quantify the deviation of a real surface from an ideally flat one. Periodically patterned surfaces, however, are an intentional deviation from that ideal. Therefore, their surface profile has to be separated into a periodic and a non-periodic part. The latter can then be analyzed using the established surface parameters and the periodic nature allows a quantification of structure homogeneity, e.g. based on Gini coefficient. This work presents a new combination of established methods to reliably and objectively evaluate periodic surface quality. For this purpose, the periodicity of a given surface is extracted by Fourier analysis, and its homogeneity with respect to a particular property is determined for the repeating element via a Gini analysis. The proposed method provides an objective and reliable instrument for evaluating the surface quality for the selected attribute regardless of the user. Additionally, this technique can potentially be used to both identify a suitable surface structuring technique and determine the optimal process parameters

Selbstfortschreitende Reaktionen in Ru/Al/X-Multilagen

Self-propagating reactions as a means for the production of intermetallic or ceramic phases belong to the reactive synthesis methods. Their systematic study started in the 1960s, just half a century ago. In contrast to most other methods, the energy required for the process is partially or fully supplied by the exothermic synthesis reaction itself which reduces or even eliminates the need for external heat sources. Its potential technological use is therefore not only the synthesis of phases but also that of a heat source e.g. for driving other reactions (“chemical oven”) or for applications in the field of joining (“reactive joining”). A distinctive feature of the self-propagating reaction is that the process is not only determined by the choice of reactants but also by their relative arrangement, shape and size. The present work investigates for the case of reactive multilayers comprising Ruthenium and Aluminum how the characteristics of the reaction (propagation speed, ignition, reaction temperature and product phases) can be modified by adding a third element. It is shown that the choice of the element and the arrangement of the layers open new opportunities for designing the reaction. By a combination of simulations and key experiments, the role of reaction characteristics for the application of reactive joining is demonstrated.Selbstfortschreitende Reaktionen zur Herstellung intermetallischer oder keramischer Phasen zählen zu den reaktiven Syntheseverfahren. Ihre systematische Erforschung begann in den 1960er Jahren, also erst vor einen halben Jahrhundert. Im Unterschied zu den meisten anderen Verfahren stammt die für den Prozess benötigte Energie überwiegend oder vollständig aus der exothermen Synthesereaktion selbst, was den Bedarf für externe Wärmequellen reduziert oder eliminiert. Ihr potentieller technologischer Nutzen liegt nicht nur in der Synthese von Phasen, sondern auch in der Nutzung als Wärmequelle, beispielsweise für weitere Reaktionen („chemischer Ofen“) oder für Anwendungen in der Füge- und Verbindungstechnik („reaktives Fügen“). Eine Besonderheit der selbstfortschreitenden Reaktionen ist, dass ihr Ablauf nicht nur von der Art der Ausgangsstoffe bestimmt wird, sondern auch von ihrer relativen Anordnung, Gestalt und Größe. Die vorliegende Arbeit untersucht anhand von reaktiven Multilagen aus Ruthenium und Aluminium, wie sich die Eigenschaften der Reaktion (Ausbreitungsgeschwindigkeit, Zündverhalten, Reaktionstemperatur und Produktphasen) durch den Einbau eines dritten Elements verändern lassen. Es wird gezeigt, dass die Wahl des Elements und die Stapelfolge der Schichten neue Möglichkeiten für das Design der Reaktion eröffnen. Durch die Verbindung von Simulationen und Schlüsselexperimenten wird die Rolle ihrer Eigenschaften für die Anwendung des reaktiven Fügens aufgezeigt.Deutsche Forschungsgemeinschaft, Ternäre Reaktivschichtsysteme auf Basis von Ru/Al Multischichte

Investigations on micro-mechanical properties of polycrystalline Ti(C,N) and Zr(C,N) coatings

Micro-mechanical properties of Ti(C,N) and Zr(C,N) coatings deposited by chemical vapor deposition on a WC-Co cemented carbide substrate were examined by micro-compression testing using a nanoindenter equipped with a flat punch. Scanning Electron Microscopy, Focused Ion Beam, Electron Backscattered Diffraction and Finite Element Modeling were combined to analyze the deformation mechanisms of the carbonitride layers at room temperature. The results revealed that Ti(C,N) undergoes a pure intergranular crack propagation and grain decohesion under uniaxial compression; whereas the fracture mode of Zr(C,N) was observed to be inter/transgranular failure with unexpected plastic deformation at room temperature.Peer ReviewedPostprint (author's final draft

Critical Assessment of Two-Dimensional Methods for the Microstructural Characterization of Cemented Carbides

Cemented carbides, or hard metals, are ceramic–metal composites usually consisting of tungsten carbide particles bound by a cobalt-based alloy. They are the backbone materials for the tooling industry, as a direct consequence of the outstanding range of property combinations, depending on their effective microstructural assemblage, i.e., the physical dimensions and relative content of their constitutive phases. Hence, reliable microstructural characterization becomes key for hard metal grade selection and quality control. This work aimed to assess the practical twodimensional characterization methods for the most important one- and two-phase properties of cemented carbides, i.e., the carbide grain size, phase fraction, carbide contiguity, and binder mean free path. Three different methods—point, line, and area analysis—were implemented to characterize four microstructurally distinct grades. The images were acquired by optical and scanning electron microscopy, with the latter through both secondary and backscattered electrons. Results were critically discussed by comparing the obtained values of properties and the different characterization methodology. Inspection technique combinations were finally ranked based on accuracy, accessibility, and operability considerations. The line method was used to analyze all the properties, the area method, for the one-phase properties, and the point method, for only the phase fraction. It was found that the combination of optical microscopy and the line analysis method was suitable for a direct inspection and rapid estimation for carbides above fine grain size. The most precise results were achieved using line analysis of the images obtained by the backscattered electrons of the scanning electron microscope

Two α subunits and one β subunit of meprin zinc-endopeptidases are differentially expressed in the zebrafish Danio rerio

Meprins are members of the astacin family of metalloproteases expressed in epithelial tissues, intestinal leukocytes and certain cancer cells. In mammals, there are two homologous subunits, which form complex glycosylated disulfide-bonded homo- and heterooligomers. Both human meprin α and meprin β cleave several basement membrane components, suggesting a role in epithelial differentiation and cell migration. There is also evidence that meprin β is involved in immune defence owing to its capability of activating interleukin-1β and the diminished mobility of intestinal leukocytes in meprin β-knockout mice. Here we show for the first time by reverse transcription PCR, immunoblotting and immunofluorescence analyses that meprins are expressed not only in mammals, but also in the zebrafish Danio rerio. In contrast to the human, mouse and rat enzymes, zebrafish meprins are encoded by three genes, corresponding to two homologous α subunits and one β subunit. Observations at both the mRNA and protein level indicate a broad distribution of meprins in zebrafish. However, there are strikingly different expression patterns of the three subunits, which is consistent with meprin expression in mammals. Hence, D. rerio appears to be a suitable model to gain insight into the basic physiological functions of meprin metalloprotease

Effect of Pretreatment on Interface Stability and Morphology of Ni/Al Hybrid Foams by in situ Microcantilever Fracture Experiment

Ni/Al hybrid foams are a new class of innovative cellular composite materials consisting of open-cell aluminium (Al) foams electrochemically coated with nanocrystalline nickel (Ni). They may be used for lightweight construction elements or as crash energy absorbers. The Ni coating strengthens the Al foam achieving an up to ten times higher energy absorption capacities compared to the Al basis foam. Cellular materials such as foams provide a strong structure-property relationship as the macroscopic material properties strongly depend on the strut geometry and the material properties of the individual struts. The interface stability between the coating and the substrate foam is the dominant contribution in the strengthening mechanism of Ni/Al hybrid foams. Hence, micromechanical characterization is an important task for the design of components made of Ni/Al hybrid foams. A strong interface corresponds to a shear-stiff connection between substrate foam and coating, whereas a soft interface allows sliding between the two phases and hence reduces the buckling stiffness of individual foam struts resulting in lower strength and energy absorption capacity of the macroscopic foam. An increased critical energy release rate for interface cracking was revealed by in situ microcantilever bending tests prepared by focused ion beam (FIB) during bending tests in the scanning electron microscope (SEM) after the chemical pretreatment of the base foam