210563 research outputs found
Sort by
Influence of Radiation Exposure on the FEL Performance at FLASH
No full textFLASH has been operated as user facility for about 14 years. In this time, the total charge accelerated and transported through the FLASH1 undulator is around 35 Coulomb. Based on detailed monitoring of the radiation loss and reference measurements on degradation of the magnetic field of the undulator, we have performed simulations to study the change in FEL performance and first comparison of the simulations with the changes we observe during operation
X-ray crystallography and molecular dynamics studies of the inclusion complexes of geraniol in β-cyclodextrin, heptakis (2,6-di-O-methyl)-β-cyclodextrin and heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin
No full textThe inclusion of the linear monoterpene, geraniol (gr) in β-cyclodextrin (β-CD), heptakis(2,6-di-O-methyl)-β-cyclodextrin (DM-β-CD) and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TM-β-CD) has been studied by X-ray crystallography and Molecular Dynamics simulations. The gr/β-CD complex crystallizes as a head-to-head dimer in the P21 space group stacking along the crystallographic a-axis in a channel packing mode. Two guest molecules are accommodated almost axially inside the dimeric cavity with their aliphatic ends laying in the interface region of the dimer facing each other and their hydroxylic ends protruding from the narrow β-CD rims. The guest molecules of the adjacent dimers in a channel are interconnected via CH ⋯O and hydrogen bonds forming an internal wire. Both the gr/DM-β-CD and gr/TM-β-CD complexes crystallize in the P212121 space group and stack along the crystallographic b-axis in a head-to-tail manner. DM-β-CD host adopts the conformation of a rigid and well-shaped open cone upon complexation, in which the guest molecule is found highly disordered over 5 sites with varying depths of immersion. The gr/DM-β-CD complex units are arranged in channels and the gr molecules within these channels are also interconnected via CH ⋯O bonds. On the other hand, TM-β-CD host is found severely distorted adopting a ‘closed’ cup-shaped conformation. The guest is partially encapsulated in the wide rim of TM-β-CD and it is found disordered over 3 sites with quite different orientations. The complex units are arranged forming screw channels, with the main part of the guest laying outside the host cavity and filling the intermediate space between the succeeding hosts. The MD analysis based on the crystallographically determined structures sheds light on the dynamic behavior of the geraniol upon complexation with these hosts, its conformation variations and the interconversion of the inclusion modes in solution. Finally, MM/GBSA-calculations revealed that the ascending order in binding affinity ΔG values is: gr/TM-β-CD < gr/DM-β-CD < gr/β-CD
Atomic structure of Ca–Mg biodegradable metallic glass
No full textVery low density eutectic Ca72Mg28 at.% alloy is a precursor of complex biodegradable alloys with potential use as bioresorbable alloy for orthopaedic applications. The structure of the amorphous alloy was investigated by using X-ray, neutron diffraction and reverse Monte Carlo (RMC) modelling. The RMC configuration was decomposed into polyhedral holes whose faces are all triangles consisting of chemical bonds. Free volumes in the respective polyhedral holes were evaluated with reference to the packing efficiency of crystalline CaMg2 HCP phase. The tetrahedral holes, accounting for about 55% of the whole space, are regarded as densely packed units because the average packing efficiency of them is approximately equal to that of the corresponding crystal phase. At the same time, various types of polyhedral holes which have a certain free volume have been observed, and some of them are connected with each other. The densely packed coordination polyhedra consisting only of tetrahedral holes tend to be clustere
Time-resolved investigation of the optical phase change as a potential diagnostics tool for extreme-ultraviolet free-electron-laser pump and optical probe experiments
No full textMeasurement of transient optical properties (reflectivity and transmissivity) is performed widely in extreme-ultraviolet (XUV) pump–optical probe experiments to study the transient state of irradiated materials. In order to extend the material diagnostics, here we propose an additional measurement of the transient phase change of the optical probe pulse. It can be recorded in parallel to other transient optical properties, enabling access to full information on the complex refractive index and thickness of the radiation-modified material layer. The latter is essential for investigations of phase transitions progressing in XUV (and x-ray) irradiated materials. We perform a computational study that clearly shows that the measurement of the optical phase from a probe pulse at correctly tuned pulse parameters can provide a signal strong enough to extract information on transient material properties. The calculations suggest that in some cases, it is even more preferable to measure the transient phase change than other optical parameters. Such phase measurement, feasible with modern experimental setups, can then be a basis for an improved diagnostics tool for the temporal characteristics of an ultrashort XUV pulse
Liquid Exfoliation of : Structural Characterization, Size-Dependent Properties, and Degradation
No full textBone Biomineral Properties Vary across Human Osteonal Bone
No full textThe biomineralization of bone remains apuzzle. During Haversian remodeling in the dense humancortical bone, osteoclasts excavate a tunnel that is then filledin by osteoblasts with layers of bone of varying fibrilorientations, resulting in a lamellar motif. Such bonerepresents an excellent possibility to increase our understandingof bone as a material as well as bonebiomineralization by studying spatio/temporal variations inthe biomineral across an osteon. To this end, fluorescencecomputed tomography and diffraction scattering computedtomography with sub-micrometer resolution is applied toobtain position resolved fluorescence spectra and diffractionpatterns in a 3D volume. The microstructural properties ofthe apatite biomineral are not homogeneous but depend critically on the time point at which it was laid down. Thisindicates that the nature of bone biomineral is highly dependent on the microenvironment during bone formation andremodeling
Thermo-physical properties of coatings in the Ti(B,N) system grown by chemical vapor deposition
No full textHard protective coatings are commonly subjected to temperatures exceeding 1000 °C, which has significant influence on their thermo-physical properties and the associated performance in application. Within the present work, temperature dependent physical properties of coatings within the Ti(B,N) system grown by chemical vapor deposition were correlated with their chemical composition. High-energy X-ray diffraction experiments in inert atmosphere proved that TiN, TiB2 and ternary TiBxNy coatings with varying B contents are thermally stable up to 1000 °C. In-plane strains of TiN and TiBxNy coatings diminish during heating, whereas TiB2 exhibits compressive strain enhancement up to the deposition temperature. Nanocrystalline TiB2 exhibits more pronounced grain growth during annealing compared to coarse grained columnar TiN. Within the investigated coatings, the mean thermal expansion coefficient decreases as the B content increases. The same trend was observed for the thermal conductivity, which correlates with the grain size of the coatings
Development of an analysis to probe the neutrino mass ordering with atmospheric neutrinos using three years of IceCube DeepCore data
No full textThe Neutrino Mass Ordering (NMO) remains one of the outstanding questions in the field of neutrino physics. One strategy to measure the NMO is to observe matter effects in the oscillation pattern of atmospheric neutrinos above , as proposed for several next-generation neutrino experiments. Moreover, the existing IceCube DeepCore detector can already explore this type of measurement. We present the development and application of two independent analyses to search for the signature of the NMO with three years of DeepCore data. These analyses include a full treatment of systematic uncertainties and a statistically-rigorous method to determine the significance for the NMO from a fit to the data. Both analyses show that the dataset is fully compatible with both mass orderings. For the more sensitive analysis, we observe a preference for normal ordering with a p-value of and for the inverted ordering hypothesis, while the experimental results from both analyses are consistent within their uncertainties. Since the result is independent of the value of and obtained from energies , it is complementary to recent results from long-baseline experiments. These analyses set the groundwork for the future of this measurement with more capable detectors, such as the IceCube Upgrade and the proposed PINGU detector
The Origin of the Six-Gluon Amplitude in Planar SYM
No full textWe study the maximally-helicity-violating (MHV) six-gluon scattering amplitude in planar super-Yang-Mills theory at finite coupling when all three cross ratios are small. It exhibits a double logarithmic scaling in the cross ratios, controlled by a handful of ``anomalous dimensions' that are functions of the coupling constant alone. Inspired by known seven-loop results at weak coupling and the integrability-based pentagon OPE, we present conjectures for the all-order resummation of these anomalous dimensions. At strong coupling, our predictions agree perfectly with the string theory analysis. Intriguingly, the simplest of these anomalous dimensions coincides with one describing the light-like limit of the octagon, namely the four-point function of large-charge BPS operators
Novel method for the angular chirp compensation of passively CEP-stable few-cycle pulses
No full textWe demonstrate a novel, energy-efficient, cost-effective simple method for seeding CEP-stable OPCPAs. We couple the CEP-stable idler of a broadband OPCPA into a hollow core Kagome fiber thus compensating for the angular chirp. We obtain either relatively narrow bandwidths with ∼36% coupling efficiency or quarter-octave spanning bandwidths with ∼2.2% coupling efficiency. We demonstrate spectral compressibility, good beam quality and CEP stability. Our source is an ideal seed for high-energy, high-average power, CEP-stable few-cycle OPCPA pulses around 2 µm, which can drive the generation of coherent soft X-ray radiation in the water window spectral region via HHG