Strain mapping of a triple junction in nanocrystalline Pd

Aberration-corrected transmission electron microscopy was used to provide structural information on a triple junction in nanocrystalline Pd. This triple junction consists of two intersecting Σ3 twin boundaries with a Σ9 grain boundary and is connected to a quadruple point via the Σ9 grain boundary. A comprehensive strain analysis of this triple junction using geometric phase analysis is presented and compared with a molecular dynamics simulation. The main results are: (i) the strain field of the core of the triple junction shows dislocation character and extends over a distance of about 0.5 nm; (ii) the intersecting boundaries result in a net translation of , which corresponds to a Burgers vector of an dislocation in the fcc lattice; (iii) a disclination emerging from the triple junction along the Σ9 grain boundary is balanced by a disclination of opposite sign emerging from the quadruple point. Based on the observation that the core of the triple junction can be described by the strain field of a dislocation, its energy was estimated using to be about 1.7 × 10⁻⁹ J m⁻¹. The presence of a disclination dipole is thought to be essential for stabilization of the structure observed.     

Structural analysis of articular cartilage using multiphoton microscopy: input for biomechanical modeling

The 3-D morphology of chicken articular cartilage was quantified using multiphoton microscopy (MPM) for use in continuum-mechanical modeling. To motivate this morphological study we propose aspects of a new, 3-D finite strain constitutive model for articular cartilage focusing on the essential load-bearing morphology: an inhomogeneous, poro-(visco)elastic solid matrix reinforced by an anisotropic, (visco)elastic dispersed fiber fabric which is saturated by an incompressible fluid residing in strain-dependent pores. Samples of fresh chicken cartilage were sectioned in three orthogonal planes and imaged using MPM, specifically imaging the collagen fibers using second harmonic generation. Employing image analysis techniques based on Fourier analysis, we derived the principal directionality and dispersion of the collagen fiber fabric in the superficial layer. In the middle layer, objective thresholding techniques were used to extract the volume fraction occupied by extracellular collagen matrix. In conjunction with information available in the literature, or additional experimental testing, we show how this data can be used to derive a 3-D map of the initial solid volume fraction and Darcy permeability.     

Frequency-domain optical tomographic imaging of arthritic finger joints

We are presenting data from the largest clinical trial on optical tomographic imaging of finger joints to date. Overall we evaluated 99 fingers of patients affected by rheumatoid arthritis (RA) and 120 fingers from healthy volunteers. Using frequency-domain imaging techniques we show that sensitivities and specificities of 0.85 and higher can be achieved in detecting RA. This is accomplished by deriving multiple optical parameters from the optical tomographic images and combining them for the statistical analysis. Parameters derived from the scattering coefficient perform slightly better than absorption derived parameters. Furthermore we found that data obtained at 600 MHz leads to better classification results than data obtained at 0 or 300 MHz.     

Biological effects of acrylamide after daily ingestion of various foods in comparison to water: a study in rats

Scope: Acrylamide (AA), classified as a genotoxic carcinogen, is generated by heating foods. We studied whether the food matrix modulates bioavailability and/or biotransformation and investigated kinetics and biological effectiveness of AA in rats. Methods and results: AA was given to the animals at a daily intake level of AA containing foods for up to 9 days, resulting in an exposure of 50 or 100 μg AA/kg body weight (b.w.)/day. Positive controls received the same dosages of AA in water, negative controls just water. As biomarkers urinary mercapturic acids, hemoglobin adducts, plasma levels of AA and glycidamide (GA) and DNA integrity in white blood cells and hepatocytes were measured. Altogether, no significant differences in bioavailability of AA from water and the different food matrices were observed. Only with bread crust, biomarkers indicated a slightly reduced bioavailability. Monitoring glycidamide valine adduct adducts did not provide evidence for treatment‐related significantly enhanced GA‐haemoglobin adduct formation in blood although glycidamide mercapturic acid excretion in urine indicated significant GA formation. Conclusions: The results suggest AA at dietary intake levels, exceeding estimated human mean intake by a factor of at least 100 to become detoxified in Sprague–Dawley rats to a major extent through glutathione coupling.     

Vibrational properties of the LiNbO3 z-surfaces

The existence of localized vibrational modes both at the positive and at the negative LiNbO3 (0001) surface is demonstrated by means of first-principles calculations and Raman spectroscopy measurements. First, the phonon modes of the crystal bulk and of the (0001) surface are calculated within the density functional theory. In a second step, the Raman spectra of LiNbO(3) bulk and of the two surfaces are measured. The phonon modes localized at the two surfaces are found to be substantially different, and are also found to differ from the bulk modes. The calculated and measured frequencies are in agreement within the error of the method. Raman spectroscopy is shown to be sensitive to differences between bulk and surface and between positive and negative surface. It represents therefore an alternative method to determine the surface polarity, which does not exploit the pyroelectric or piezoelectric properties of the material.     

Photocatalytic TiO2 films deposited by different methods

Photocatalytic TiO₂ layers are deposited with different methods available within the Fraunhofer Photocatalysis Alliance. These are: Magnetron sputtering, evaporation, sol‐gel, laquer coating, and CVD. The photocatalytic activity under UV illumination is determined by decomposition of stearic acid. The optical properties of the films are compared and discussed.     

Short wavelength emission of AlGaInP quantum dots grown on GaP substrate

We report on the growth of AlGaInP quantum dots (QDs) with Al contents between 0% and 10% on GaP substrate by gas-source molecular beam epitaxy and the investigation of their morphological and low temperature photoluminescence properties. These high areal density QDs show short wavelength emission between 575 and 612 nm depending on their composition. The authors interpret the QD emission as originating from indirect type-II transitions. This interpretation is supported by a single-band effective-mass model, which allows us to describe the role of differing barrier composition in the QD emission. Time-resolved photoluminescence measurements are performed and discussed with respect to the calculations.     

Cleaved-edge-overgrowth nanogap electrodes

We present a method to fabricate multiple metal nanogap electrodes of tailored width and distance in parallel, on the cleaved plane of a GaAs/AlGaAs heterostructure. The three-dimensional patterned structures are obtained by a combination of molecular-beam-epitaxial regrowth on a crystal facet, using the cleaved-edge-overgrowth (CEO) method, and subsequent wet selective etching and metallization steps. SEM and AFM studies reveal smooth and co-planar electrodes of width and distance of the order of 10 nm. Preliminary electrical characterization indicates electrical gap insulation in the 100 MΩ range with kΩ lead resistance. We propose our methodology to realize multiple electrode geometries that would allow investigation of the electrical conductivity of complex nanoscale objects such as branched organic molecules.     

Re-evaluation of correction factors of a primary standard graphite calorimeter in 60Co gamma ray beams as a basis for the appointment of the BEV absorbed dose rate to water reference value

The graphite calorimeter of the Federal Office of Metrology and Surveying (BEV-Bundesamt für Eich- und Vermessungswesen) was established in the 1980s as the primary standard for the absorbed dose to water for (60)Co gamma ray beams. To maintain the primary standard at an international level the graphite calorimeter and its corresponding components had to undergo a refurbishment and modernisation process. The correction factors of the graphite calorimeter were re-evaluated with Monte Carlo and experimental methods to obtain improved values. These are the correction for the effect of the gaps (1.0061), the scaling correction (0.9998), the correction for the difference in air attenuation (0.9971) and the corrections for the effective measurement depths in the graphite phantom for the graphite calorimeter (0.9886) and the CC01-105 ionisation chamber (0.9913). Consequently, it was necessary to change the reference value for the absorbed dose rate to water of the (60)Co teletherapy unit used for the calibration of secondary standard dosemeters.     

Bioresponse-guided decomposition of roast coffee beverage and identification of key bitter taste compounds

Sensory-guided fractionation of a roasted coffee brew by means of sequential solvent extraction, ultrafiltration, and RP-HPLC demonstrated a group of ethyl acetate soluble compounds formed from O-hydroxycinnamoyl quinic acid derivatives upon coffee roasting as the key compounds contributing to the bitter taste of roasted coffee beverages. LC-MS/MS studies, 1D- and 2D-NMR spectroscopy, syntheses, and model roast experiments with 5-O-caffeoyl- and 5-O-feruloylquinic acid led to the unequivocal identification of 3-O-caffeoyl-γ-quinide (2a), 4-O-caffeoyl-γ-quinide (3a), 5-O-caffeoyl-epi-δ-quinide (4a), 4-O-caffeoyl-muco-γ-quinide (5a), 5-O-caffeoyl-muco-γ-quinide (6a), 3-O-feruloyl-γ-quinide (2b), and 4-O-feruloyl-γ-quinide (3b) as intense coffee bitter tastants. Besides these individual bitter compounds, a highly complex and intensely bitter HPLC fraction was isolated from the ethyl acetate extractables of coffee brew. Application of COSY spectroscopy and alkaline hydrolytic degradation gave strong evidence that the bitter taste of that fraction is due to a multiplicity of rather complex quinic acid lactone isomers multiply esterified with p-coumaric acid, caffeic acid, ferulic acid, 3,4-dimethoxycinnamic acid, and quinic acid, respectively. As representatives of this fraction, 3,4-O-dicaffeoyl-γ-quinide (10), 3,5-O-dicaffeoyl-epi-δ-quinide (11), and 4,5-O-dicaffeoyl-muco-γ-quinide (12) have been isolated, purified, and identified as strongly bitter-tasting compounds in roasted coffee. For the first time, bitter taste recognition thresholds were determined for the individual compounds showing that, strongly depending on their chemical structure, the bitter threshold levels ranged between 9.8 and 180 μmol/l (water).