Keratin homogeneity in the tail feathers of Pavo cristatus and Pavo cristatus mut. alba

The keratin structure in the cortex of peacocks' feathers is studied by X-ray diffraction along the feather, from the calamus to the tip. It changes considerably over the first 5. cm close to the calamus and remains constant for about 1. m along the length of the feather. Close to the tip, the structure loses its high degree of order. We attribute the X-ray patterns to a shrinkage of a cylindrical arrangement of β-sheets, which is not fully formed initially. In the final structure, the crystalline beta-cores are fixed by the rest of the keratin molecule. The hydrophobic residues of the beta-core are locked into a zip-like arrangement. Structurally there is no difference between the blue and the white bird. © 2010 Elsevier Inc

Mid-infrared interference coatings with excess optical loss below 10 ppm

Low excess optical loss, combined absorption and scatter loss, is a key performance metric for any high-reflectance coating technology and is currently one of the main limiting factors for the application of optical resonators in the mid-infrared spectral region. Here we present high-reflectivity substrate-transferred single-crystal GaAs/AlGaAs interference coatings at a center wavelength of 4.54 µm with record-low excess optical loss below 10 parts per million. These high-performance mirrors are realized via a novel microfabrication process that differs significantly from the production of amorphous multilayers generated via physical vapor deposition processes. This new process enables reduced scatter loss due to the low surface and interfacial roughness, while low background doping in epitaxial growth ensures strongly reduced absorption. We report on a suite of optical measurements, including cavity ring-down, transmittance spectroscopy, and direct absorption tests to reveal the optical losses for a set of prototype mirrors. In the course of these measurements, we observe a unique polarization-orientation-dependent loss mechanism which we attribute to elastic anisotropy of these strained epitaxial multilayers. A future increase in layer count and a corresponding reduction of transmittance will enable optical resonators with a finesse in excess of 100,000 in the mid-infrared spectral region, allowing for advances in high-resolution spectroscopy, narrow-linewidth laser stabilization, and ultrasensitive measurements of various light–matter interactions

On the valid frequency range of Timoshenko beam theory

The frequency equation of Timoshenko beam theory factorises for hinged-hinged end conditions, leading to a first and second spectrum of natural frequencies; the latter is largely inaccurate and can be isolated and disregarded. For the majority of other end conditions, when the frequency equation does not factorise, one may think in terms of pseudo-second spectrum contributions arising when evanescent waves become propagating above the cut-off frequency , and it is conjectured that these may have a corrupting effect on the frequency predictions. Comparisons with measured and simulated frequencies lead to the conclusion that Timoshenko predictions above the cut-off frequency should be disregarded for those end conditions for which the frequency equation does not factorise

Structural properties of mirrored carbon spirals as revealed by scanning electron microscopy and micro-raman spectroscopy

A novel type of iron-carbon composite nano-structures has been synthesised from a pressurized ferrocene vapor. Scanning electron microscopy shows that the nano-structures are produced in large yield and high purity. Their unique morphology is manifested by high reflectional symmetry, composed of two conical arms spiralling out of an almost spherical core. The size extends to 40μm in length with the arm's tips as thin as 100nm. In the micrograph, the core area shows brighter contrasts than the arms, indicating its iron richness. Micro-Raman spectroscopy across the sample surface unravels that the graphitic arms encapsulate the iron core entirely. Such unique encapsulated nano-composites with defined shapes could be useful in many applications. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Structural properties of mirrored carbon spirals as revealed by scanning electron microscopy and micro-raman spectroscopy

A novel type of iron-carbon composite nano-structures has been synthesised from a pressurized ferrocene vapor. Scanning electron microscopy shows that the nano-structures are produced in large yield and high purity. Their unique morphology is manifested by high reflectional symmetry, composed of two conical arms spiralling out of an almost spherical core. The size extends to 40μm in length with the arm's tips as thin as 100nm. In the micrograph, the core area shows brighter contrasts than the arms, indicating its iron richness. Micro-Raman spectroscopy across the sample surface unravels that the graphitic arms encapsulate the iron core entirely. Such unique encapsulated nano-composites with defined shapes could be useful in many applications. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim