Paramagnetic signature of microcrystalline silicon carbide

Abstract. The most important challenge on the way to optimized solar cells is to make the thickness of the individual layers smaller than the diffusion length of the charge carriers, in order to keep the collection efficiency close to unity. Here, we propose ß-SiC microcrystals grown by a sol-gel based process as a promising acceptor material. The samples are characterized by optical spectroscopy and electron paramagnetic resonance (EPR). With the help of band structures for selected surface states calculated in the framework of density functional theory (DFT) a possible scenario for the observed acceptor process is discussed

Subcellular localization of PD‐L1 and cell‐cycle‐dependent expression of nuclear PD‐L1 variants: implications for head and neck cancer cell functions and therapeutic efficacy

The programmed cell death 1 ligand 1 (PD-L1)/programmed cell death protein 1 (PD-1) axis is primarily associated with immunosuppression in cytotoxic T lymphocytes (CTLs). However, mounting evidence is supporting the thesis that PD-L1 not only functions as a ligand but mediates additional cellular functions in tumor cells. Moreover, it has been demonstrated that PD-L1 is not exclusively localized at the cellular membrane. Subcellular fractionation revealed the presence of PD-L1 in various cellular compartments of six well-characterized head and neck cancer (HNC) cell lines, including the nucleus. Via Western blotting, we detected PD-L1 in its well-known glycosylated/deglycosylated state at 40–55 kDa. In addition, we detected previously unknown PD-L1 variants with a molecular weight at approximately 70 and > 150 kDa exclusively in nuclear protein fractions. These in vitro findings were confirmed with primary tumor samples from head and neck squamous cell carcinoma (HNSCC) patients. Furthermore, we demonstrated that nuclear PD-L1 variant expression is cell-cycle-dependent. Immunofluorescence staining of PD-L1 in different cell cycle phases of synchronized HNC cells supported these observations. Mechanisms of nuclear PD-L1 trafficking remain less understood; however, proximity ligation assays showed a cell-cycle-dependent interaction of the cytoskeletal protein vimentin with PD-L1, whereas vimentin could serve as a potential shuttle for nuclear PD-L1 transportation. Mass spectrometry after PD-L1 co-immunoprecipitation, followed by gene ontology analysis, indicated interaction of nuclear PD-L1 with proteins involved in DNA remodeling and messenger RNA (mRNA) splicing. Our results in HNC cells suggest a highly complex regulation of PD-L1 and multiple tumor cell-intrinsic functions, independent of immune regulation. These observations bear significant implications for the therapeutic efficacy of immune checkpoint inhibition

Zircon geochronology, elemental and Sr-Nd isotope geochemistry of two Variscan granitoids from the Odenwald-Spessart crystalline complex (mid-German crystalline rise)

The crystalline parts of the Bergsträsser (western) Odenwald and the southern Spessart expose Variscan I-type granitoids of the mid-German crystalline rise that formed during subduction of the Rheic ocean and collision of Avalonia and Armorica about 365 and 330 Ma ago. We present geochemical, Sr-Nd isotopic, single zircon 207Pb/206Pb evaporation and conventional U-Pb data from a diorite-granodiorite complex of the southern Spessart and from a flasergranitoid of the Bergsträsser Odenwald unit II. Both intrusions provide almost identical zircon ages (332.4 ± 1.6 Ma for Odenwald and 330.4 ± 2.0 Ma for Spessart). Lack of inherited or pre-magmatic zircon components connotes magma genesis in deep crustal hot zones despite low temperature estimates (758–786 °C) derived from zircon saturation thermometry. Investigated rock samples display normal- to high-K calc-alkaline metaluminous (Spessart) and weakly peraluminous (Odenwald) geochemical characteristics. The Spessart pluton has lower εNd(T) values (−2.3 to −3.0) and higher 87Sr/86Sri ratios (0.7060 to 0.7066) compared to Odenwald flasergranitoid (εNd(T) = −0.8 and 87Sr/86Sri = 0.7048). In terms of the tectonic setting, the diorite-granodiorite complex of the southern Spessart forms the continuation of the north Armorican arc segment exposed in the Bergsträsser Odenwald. Taking into account previously reported geochemical and isotopic results, it is concluded that the Spessart pluton does not match compositions of Odenwald unit II granitoids but likely represents the north-eastward extension of unit III

Zircon response to high-grade metamorphism as revealed by U-Pb and cathodoluminescence studies

Correct interpretation of zircon ages from high-grade metamorphic terrains poses a major challenge because of the differential response of the U-Pb system to metamorphism, and many aspects like pressure-temperature conditions, metamorphic mineral transformations and textural properties of the zircon crystals have to be explored. A large (c. 450 km2) coherent migmatite complex was recently discovered in the Bohemian Massif, Central European Variscides. Rocks from this complex are characterized by granulite- and amphibolite-facies mineral assemblages and, based on compositional and isotopic trends, are identified as the remnants of a magma body derived from mixing between tonalite and supracrustal rocks. Zircon crystals from the migmatites are exclusively large (200-400 µm) and yield 207Pb/206Pb evaporation ages between 342-328 Ma and single-grain zircon fractions analysed by U-Pb ID-TIMS method plot along the concordia curve between 342 and 325 Ma. High-resolution U-Pb SHRIMP analyses substantiate the existence of a resolvable age variability and yield older 206Pb/238U ages (342-330 Ma, weighted mean age = 333.6 ± 3.1 Ma) for inner zone domains without relict cores and younger 206Pb/238U ages (333-320 Ma, weighted mean age = 326.0 ± 2.8 Ma) for rim domains. Pre-metamorphic cores were identified only in one sample (206Pb/238U ages at 375.0 ± 3.9, 420.3 ± 4.4 and 426.2 ± 4.4 Ma). Most zircon ages bracket the time span between granulite-facies metamorphism in the Bohemian Massif (~345 Ma) and the late-Variscan anatectic overprint (Bavarian phase, ~325 Ma). It is argued that pre-existing zircon was variously affected by these metamorphic events and that primary magmatic growth zones were replaced by secondary textures as a result of diffusion reaction processes and replacement of zircon by dissolution and recrystallization followed by new zircon rim growth. Collectively, the results show that the zircons equilibrated during high-grade metamorphism and record partial loss of radiogenic Pb during post-peak granulite events and new growth under subsequent anatectic conditions. © 2012 Springer-Verlag

Characterization of fiber matrix interface of continuous-discontinuous fiber reinforced polymers on the microscale

In lightweight constructions fiber reinforced polymers are an important material group. They combine low density with high strength and stiffness. The characterization of fiber reinforced polymers includes the characterization of the fibers, the matrix and the intermediate interface. The fibers and the matrix can be characterized on the neat materials. Single fiber tests are typically used to characterize the interface. However, the interaction between different fibers inside a composite is not taken into account in a single fiber test. The investigated sheet molding compound (SMC) has a bundle arrangement of the fibers, where the contact of different fibers is very close and therefore also the fiber-fiber interaction has a high influence. Here we investigate the micromechanical behavior o f hourglass shaped micro specimens with several hundreds of fibers with quasistatic tensile tests. For the interface characterization the microstructure of the specimens is rebuilt in a simulation. The glass fibers are modeled as linear elastic, the matrix as hyperelastic and the interface by means of a cohesive zone model

Atomic Structure of Interface States in Silicon Heterojunction Solar Cells

Combining orientation dependent electrically detected magnetic resonance EDMR and g tensor calculations based on density functional theory DFT we assign microscopic structures to paramagnetic states involved in spin dependent recombination at the interface of amorphous crystalline silicon a Si H c Si heterojunction solar cells. We find that i the interface exhibits microscopic roughness, ii the electronic structure of the interface defects is mainly determined by c Si, iii identify the microscopic origin of the conduction band tail state in the a Si H layer and iv propose a detailed recombination mechanis

The Erbisberg drilling 2011: Implications for the structure and postimpact evolution of the inner ring of the Ries impact crater

The 26 km diameter Nördlinger Ries is a complex impact structure with a ring structure that resembles a peak ring. A first research drilling through this “inner crystalline ring” of the Ries was performed at the Erbisberg hill (SW Ries) to better understand the internal structure and lithology of this feature, and possibly reveal impact‐induced hydrothermal alteration. The drill core intersected the slope of a 22 m thick postimpact travertine mound, before entering 42 m of blocks and breccias of crystalline rocks excavated from the Variscan basement at >500 m depth. Weakly shocked gneiss blocks that show that shock pressure did not exceed 5 GPa occur above polymict lithic breccias of shock stage Ia (10–20 GPa), with planar fractures and planar deformation features (PDFs) in quartz. Only a narrow zone at 49.20–50.00 m core depth exhibits strong mosaicism in feldspar and {102} PDFs in quartz, which are indicative of shock stage Ib (20–35 GPa). Finally, 2 m of brecciated Keuper sediments at the base of the section point to an inverse layering of strata. While reverse grading of clast sizes in lithic breccias and gneiss blocks is consistent with lateral transport, the absence of diaplectic glass and melt products argues against dynamic overthrusting of material from a collapsing central peak, as seen in the much larger Chicxulub structure. Indeed, weakly shocked gneiss blocks are rather of local provenance (i.e., the transient crater wall), whereas moderately shocked polymict lithic breccias with geochemical composition and 87Sr/86Sr signature similar to Ries suevite were derived from a position closer to the impact center. Thus, the inner ring of the Ries is formed by moderately shocked polymict lithic breccias likely injected into the transient crater wall during the excavation stage and weakly shocked gneiss blocks of the collapsing transient crater wall that were emplaced during the modification stage. While the presence of an overturned flap is not evident from the Erbisberg drilling, a survey of all drillings at or near the inner ring point to inverted strata throughout its outer limb. Whether the central ring of the Ries represents remains of a collapsed central peak remains to be shown. Postimpact hydrothermal alteration along the Erbisberg section comprises chloritization, sulfide veinlets, and strong carbonatization. In addition, a narrow zone in the lower parts of the polymict lithic breccia sequence shows a positive Eu anomaly in its carbonate phase. The surface expression of this hydrothermal activity, i.e., the travertine mound, comprises subaerial as well as subaquatic growth phases. Intercalated lake sediments equivalent to the early parts of the evolution of the central crater basin succession confirm a persistent impact‐generated hydrothermal activity, although for less time than previously suggested