X-ray high-resolution diffraction using refractive lenses

Refractive x-ray lenses have recently been applied for imaging and scanning microscopy with hard x rays. We report the application of refractive lenses in an optical scheme for high-resolution x-ray diffraction, performed at a high brilliance synchrotron radiation source. An experimental proof of principle and a theoretical discussion are presented. In particular, we observe the x-ray diffraction pattern from a two-dimensional photonic crystal with 4.2 µm periodicity, which normally is employed to scatter light in the infrared

Herkommer zum Hinschauen

Tagung: Moderne Architektur exemplarisch. Hans Herkommer (1887-1956). Technische Universität Kaiserslautern, Lehrgebiet Geschichte und Theorie der Architektur. Prof. Dr. phil. Matthias Schirren. 28.-29. Oktober 201

Cutting a Cake Is Not Always a 'Piece of Cake': A Closer Look at the Foundations of Cake-Cutting Through the Lens of Measure Theory

Cake-cutting is a playful name for the fair division of a heterogeneous, divisible good among agents, a well-studied problem at the intersection of mathematics, economics, and artificial intelligence. The cake-cutting literature is rich and edifying. However, different model assumptions are made in its many papers, in particular regarding the set of allowed pieces of cake that are to be distributed among the agents and regarding the agents' valuation functions by which they measure these pieces. We survey the commonly used definitions in the cake-cutting literature, highlight their strengths and weaknesses, and make some recommendations on what definitions could be most reasonably used when looking through the lens of measure theory

Electronic properties of wurtzite GaAs: A correlated structural, optical, and theoretical analysis of the same polytypic GaAs nanowire

III-V compound semiconductor nanowires are generally characterized by the coexistence of zincblende and wurtzite structures. So far, this polytypism has impeded the determination of the electronic properties of the metastable wurtzite phase of GaAs, which thus remain highly controversial. In an effort to obtain new insights into this topic, we cross-correlate nanoscale spectral imaging by near-field scanning optical microscopy with a transmission electron microscopy analysis of the very same polytypic GaAs nanowire dispersed onto a Si wafer. Thus, spatially resolved photoluminescence spectra could be unambiguously assigned to nanowire segments whose structure is known with lattice-resolved accuracy. An emission energy of 1.528 eV was observed from extended zincblende segments, revealing that the dispersed nanowire was under uniaxial strain presumably due to interaction with its supporting substrate. These crucial information and the emission energy obtained for extended pure wurtzite segments were used to perform envelope function calculations of zincblende quantum disks in a wurtzite matrix as well as the inverse structure. In these calculations, we varied the fundamental bandgap, the electron mass, and the band offset between zincblende and wurtzite GaAs. From this multi-parameter comparison with the experimental data, we deduced that the bandgap between the Γ8 conduction and A valence band ranges from 1.532 to 1.539 eV in strain-free wurtzite GaAs, and estimated values of 1.507 to 1.514 eV for the Γ7–A bandgap. Address correspondenc

Untersuchung zum molekularen Mechanismus der chemisch Induzierten Resistenz in Gerste (Hordeum vulgare L.) gegenüber dem Echten Gerstenmehltaupilz (Blumeria graminis f. sp. hordei)

Durch die Applikation von chemischen Resistenzinduktoren kommt es in anfälligen Gerstensorten zu einer deutlich erhöhten systemischen Resistenz gegenüber dem Echten Gerstenmehltaupilz (Blumeria graminis f. sp. hordei, Bgh). Es sollten Gene identifiziert werden, die ursächlich an der Ausbildung dieser Form der Resistenz beteiligt sind und dadurch zur Aufklärung der beteiligten Signalwege beigetragen werden. Unter Verwendung von cDNA-Arrays wurden aus 1536 Genfragmenten 28 Gene identifiziert, die bislang nicht als chemisch induzierbar beschrieben waren. Für fünf dieser Gene wurde die Induzierbarkeit durch two step RT-PCRs bestätigt. Es handelt sich dabei um drei Gene mit bislang unbekannter Funktion, ein Gen mit Homologie zu Reticulon-ähnlichen Genen und eine Cysteinprotease. Ihre Beteiligung an der Resistenz der Gerste gegenüber Bgh wurde mittels transienten knock downs untersucht. Keines der unter¬suchten Gene scheint als Einzelfaktor für eine erfolgreiche Abwehrreaktion erforderlich zu sein. Ein sequenzhomologes Gerstengen zu AtEds5, welches in Arabidopsis ursächlich an der pathogen-induzierten SA-Produktion und SAR beteiligt ist, wurde ebenfalls in Gerste transient ausgeschaltet, um seine Beteiligung an der Resistenzausprägung zu überprüfen. Außerdem wurde die Funktion von HvSgt1 während der cIR in Gerste untersucht, da für Sgt1 in Gerste bereits eine Beteiligung an der R-Gen-vermittelten Resistenz gezeigt werden konnte. Des Weiteren wurden die chemisch induzierbaren Gene Bci2, ein blattspezifisches Thionin, Bci4, ein EF-hand Protein und Bci9, eine saure Phosphatase funktionell untersucht. Es standen stabil transgene Pflanzen zur Verfügung, die Bci4 überexprimieren, während Bci2 und Bci9 im transienten Transformationsassay untersucht wurden. Die transienten knock downs von Eds5 und Sgt1 haben keinen Einfluss auf die Penetrationseffizienz von Bgh. Für Bci4 und Bci9 konnte kein signifikanter Einfluss auf die Gersten-Mehltau Interaktion nachgewiesen werden, während der transiente knock down von Bci2 in BTH-behandelten Gerstenblättern zu einer erhöhten Suszeptibiltät gegenüber Bgh führt. Die Ergebnisse zeigen, dass sich cDNA-Arrays eher zur Expressionsanalyse, d. h. zur Analyse der Veränderungen in der Zelle, die zur metabolischen Adaption an die Induzierte Resistenz führen, aber nicht unbedingt zur Identifizierung ursächlich an der Resistenzausprägung beteiligter Gene in Gerste eignen. Dazu wäre die Analyse von Mutanten, wie in A. thaliana seit mehreren Jahren praktiziert, besser geeignet. Allerdings ist die Generierung von T-DNA-Insertionslinien in großem Maßstab in Gerste erst in den Anfängen.The application of chemical resistance inducers leads in susceptible barley lines to higher resistance against the infection with the barley powdery mildew fungus (Blumeria graminis f. sp. hordei, Bgh). Since the signal transduction pathways of the chemical induced resistance (cIR) in monocotyledonous plants are poorly understood, the aim of this work was to identify genes that are causally related to this kind of resistance. Using cDNA-arrays with 1536 gene fragments 28 new genes were identified, that were not described before to be chemical inducible. Five of them could be verified to be chemical inducible using the method of two-step RT-PCR. The functions of three of these genes have until now not been described, one shares homology with reticulon-like genes and one is a cysteine protease. The function of the five genes according the resistance of barley against Bgh was tested using a transient transformation system for silencing the gene expression. None of the tested genes as a single factor seems to have an influence on the pathogen response. A barley gene that shows highest homology to AtEds5, which causally involved in SA-production and SAR, was also transiently knocked down to check its involvement in resistance against Bgh. HvSgt1 was also tested using transient knock down, because it is involved in the R-gene mediated resistance in barley. Additionally the function of Bci2, a leaf-specific thionin, Bci4, an EF-hand protein and Bci9, an acid phosphatase were checked. Bci4 overexpressing cereal plants were available, while Bci2 and Bci9 were checked in transient transformation assays. Transient knock downs of the Eds5-homologue and HvSgt1 have no effect on penetration efficiency of Bgh. Overexpression of the three Bci-genes has also no effect on the resistance against Bgh. Just the transient knock down of Bci2 in BTH-treated barley leaves lead to higher susceptibility against Bgh. cDNA-arrays are a good tool for expression analysis in barley, e. g. for the changes concerning metabolic adaptation to the induced resistance, but they are not suitable for the identification of genes that are causally related to resistance in barley. A mutant screen as it is done in A. thaliana for many years would more appropriate. But the construction of mutant libraries in barley is still on the way

The radiosensitizing effect of platinum nanoparticles in proton irradiations is not caused by an enhanced proton energy deposition at the macroscopic scale

Objective. Due to the radiosensitizing effect of biocompatible noble metal nanoparticles (NPs), their administration is considered to potentially increase tumor control in radiotherapy. The underlying physical, chemical and biological mechanisms of the NPs' radiosensitivity especially when interacting with proton radiation is not conclusive. In the following work, the energy deposition of protons in matter containing platinum nanoparticles (PtNPs) is experimentally investigated. Approach. Surfactant-free monomodal PtNPs with a mean diameter of (40 ± 10) nm and a concentration of 300 μg ml−1, demonstrably leading to a substantial production of reactive oxygen species (ROS), were homogeneously dispersed into cubic gelatin samples serving as tissue-like phantoms. Gelatin samples without PtNPs were used as control. The samples' dimensions and contrast of the PtNPs were verified in a clinical computed tomography scanner. Fields from a clinical proton machine were used for depth dose and stopping power measurements downstream of both samples types. These experiments were performed with a variety of detectors at a pencil beam scanning beam line as well as a passive beam line with proton energies from about 56–200 MeV. Main results. The samples' water equivalent ratios in terms of proton stopping as well as the mean proton energy deposition downstream of the samples with ROS-producing PtNPs compared to the samples without PtNPs showed no differences within the experimental uncertainties of about 2%. Significance. This study serves as experimental proof that the radiosensitizing effect of biocompatible PtNPs is not due to a macroscopically increased proton energy deposition, but is more likely caused by a catalytic effect of the PtNPs. Thus, these experiments provide a contribution to the highly discussed radiobiological question of the proton therapy efficiency with noble metal NPs and facilitate initial evidence that the dose calculation in treatment planning is straightforward and not affected by the presence of sensitizing PtNPs

I-BEAT: New ultrasonic method for single bunch measurement of ion energy distribution

The shape of a wave carries all information about the spatial and temporal structure of its source, given that the medium and its properties are known. Most modern imaging methods seek to utilize this nature of waves originating from Huygens' principle. We discuss the retrieval of the complete kinetic energy distribution from the acoustic trace that is recorded when a short ion bunch deposits its energy in water. This novel method, which we refer to as Ion-Bunch Energy Acoustic Tracing (I-BEAT), is a generalization of the ionoacoustic approach. Featuring compactness, simple operation, indestructibility and high dynamic ranges in energy and intensity, I-BEAT is a promising approach to meet the needs of petawatt-class laser-based ion accelerators. With its capability of completely monitoring a single, focused proton bunch with prompt readout it, is expected to have particular impact for experiments and applications using ultrashort ion bunches in high flux regimes. We demonstrate its functionality using it with two laser-driven ion sources for quantitative determination of the kinetic energy distribution of single, focused proton bunches.Comment: Paper: 17 Pages, 3 figures Supplementary Material 16 pages, 7 figure