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There is increased interest in the use of cellulose nanomaterials for the mechanical reinforcement of composites due to their high stiffness and strength. However, challenges remain in accurately determining their distribution within composite microstructures. We report the use of a range of techniques used to image aggregates of cellulose nanocrystals (CNCs) greater than 10 µm2 within a model thermoplastic polymer. While Raman imaging accurately determines CNC aggregate size, it requires extended periods of analysis and the limited observable area results in poor reproducibility. In contrast, staining the CNCs with a fluorophore enables rapid acquisition with high reproducibility, but overestimates the aggregate size as CNC content increases. Multi-channel spectral confocal laser scanning microscopy is presented as an alternative technique that combines the accuracy of Raman imaging with the speed and reproducibility of conventional confocal laser scanning microscopy, enabling the rapid determination of CNC aggregate distribution within composites.
The question of the title of Commission 24, obviously, offers a difficult problem as already mentioned in recent reports. Photographic Astrometry no longer describes the whole scope of the commission. This problem has continued during the last three years especially in view of the preparations for the astrometric tasks of the NASA Space Telescope and of the ESA satellite HIPPARCOS.
The Astrophysics Data System (ADS) is an integral part of the Astronomy Digital Library and the collaboration Urania. It provides access to 1 million references and connects these references with many other information centers and their data, such as on-line journals, object databases, and scanned journal articles. This article describes some of the features and links between the ADS and other on-line services.
This article provides expert opinion on the use of cardiovascular magnetic resonance (CMR) in young patients with congenital heart disease (CHD) and in specific clinical situations. As peculiar challenges apply to imaging children, paediatric aspects are repeatedly discussed. The first section of the paper addresses settings and techniques, including the basic sequences used in paediatric CMR, safety, and sedation. In the second section, the indication, application, and clinical relevance of CMR in the most frequent CHD are discussed in detail. In the current era of multimodality imaging, the strengths of CMR are compared with other imaging modalities. At the end of each chapter, a brief summary with expert consensus key points is provided. The recommendations provided are strongly clinically oriented. The paper addresses not only imagers performing CMR, but also clinical cardiologists who want to know which information can be obtained by CMR and how to integrate it in clinical decision-making.
Sexual violence and wartime rapes are prevalent crimes in violent conflicts all over the world. Processes of reconciliation are growing challenges in post-conflict settings. Despite this, so far few studies have examined the psychological consequences and their mediating factors. Our study aimed at investigating the degree of longtime readiness to reconcile and its associations with post-traumatic distress within a sample of German women who experienced wartime rapes in 1945.
A total of 23 wartime rape survivors were compared to age- and gender-matched controls with WWII-related non-sexual traumatic experiences. Readiness to reconcile was assessed with the Readiness to Reconcile Inventory (RRI-13). The German version of the Post-traumatic Diagnostic Scale (PDS) was used to assess post-traumatic stress disorder (PTSD) symptomatology.
Readiness to reconcile in wartime rape survivors was higher in those women who reported less post-traumatic distress, whereas the subscale “openness to interaction” showed the strongest association with post-traumatic symptomatology. Moreover, wartime rape survivors reported fewer feelings of revenge than women who experienced other traumatization in WWII.
Our results are in line with previous research, indicating that readiness to reconcile impacts healing processes in the context of conflict-related traumatic experiences. Based on the long-lasting post-traumatic symptomatology we observed that our findings highlight the need for psychological treatment of wartime rape survivors worldwide, whereas future research should continue focusing on reconciliation within the therapeutic process.
Degradation of the catalyst and catalyst support is an essential limitation of polymer electrolyte membrane (PEM) fuel cells containing commercial platinum on carbon catalysts. Catalysts based on platinum nanoparticles coated onto nanostructured TiO2 materials are presently investigated as a more stable and equally cost effective alternative. Reported here is the synthesis of two different Pt/Nb0.1Ti0.9O2 catalysts that were prepared by chemical reduction of H2PtCl6 with either sodium borohydride in ethanolic surfactant solution or ethylene glycol. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy confirmed the deposition of Pt nanoparticles on the surface of the nanofibers and revealed average sizes of 5.4 nm and 7.6 nm for reduction with ethylene glycol and sodium borohydride, respectively. The formation of smaller sized Pt nanoparticles in ethylene glycol is reasoned with the passivation of the nanoparticle surface by glycolic anions. Cyclic voltammetry measurements confirmed a higher electrochemical specific surface area (ESCA) of about 5.45 m2/gPt for the catalyst with smaller nanoparticles while the other catalyst reached only 4.96m2/gPt. Both catalysts retain about 60% of their electrochemically active surface area after 1000 voltammetric cycles in the range of 0.03 to 1.4 V vs. RHE. This relatively high value of activity retention is explained with a strong interaction between Pt nanoparticles and Nb0.1Ti0.9O2 support.
Thin polyethersulfone (PES) films were irradiated with boron ions at doses between 1013-1016B+/cm2 and energies of 50, 130 and 180 keV. The induced changes of structural and optical properties were studied in detail. The influence on sensoric properties (moisture uptake, conductivity) was also in the focus of interest. The results of vibrational spectroscopy and X-ray photoelectron spectroscopy (XPS) indicate that in dependence on dose and energy of implanted boron ions the sulfone bonds are destroyed, and carbon-rich, amorphous and graphite-like structures are formed. This structural changes cause an increase of the conductivity of the surface films to a value of 10−8 Ω−1 at a dose of 1016 B+/cm2 from an as- prepared value of 10−15 Ω −1 and an increase of the saturation concentration during the moisture uptake.
Thin films of aromatic polymers such as polyimide (PI) and polyethersulfone (PES) find an extensive use in aerospace and electronic applications, in particular, as sensitive to moisture and gas uptake layers for bimorphic sensors. In this work, a complex investigation of the film composition, microstructure and physical properties of ion beam modified polymer films was carried out to optimize the moisture uptake. To modify thin films of polyimide and polyethersulfone 50, 130 and 180 keV boron ions with irradiation doses between 1013 and 1016 B+/cm2 were implanted. It could be shown, that partly destruction of chemical bonding under ion bombardment leads to the creation of new amorphous and graphite-like structures, which increase the modified surface film conductivity by several orders of magnitude and enhances the sensitivity of these nanocomposite films to moisture uptake.
The molecular deformation of both silkworm (Bombyx mori) and spider dragline (Nephila edulis) silks has been studied using a combination of mechanical testing and Raman spectroscopy. It was found that both materials have well-defined Raman spectra and that some of the bands in the spectra shift to lower wavenumber under the action of tensile stress or strain. The band shift was linearly dependent upon stress for both types of silk fiber for the 1085/1095 cm-1 band. This observation provides a unique insight into the effect of tensile deformation upon molecular structure and the relationship between structure and mechanical properties. The measurement of micromechanical deformation within samples of wood, flax and hemp fibers using Raman spectroscopy is also reported. Upon tensile deformation of the samples it was found that the characteristic Raman peak for cellulose, located at 1095 cm-1, shifted towards a lower wavenumber, indicating that the polymer chains within the cellulose were also being deformed. The magnitude of the shift with strain was found to be similar for all samples. No shift occurred of the peak that is characteristic of the non-load-bearing lignin (1600 cm-1) in the wood samples due to its amorphous structure. The similarities between the Raman band shifts in silk and cellulose are discussed.
For Rapid Thermal Processing one of the essential problems is the dynamical temperature controlling to reduce temperature nonhomogeneities during heating up and cooling down, which are responsible for layer nonhomogeneities and slip generation. A pyrometer row consisting of five sensors is used for temperature distribution measurement in radial direction, which allows to investigate the dynamical behaviour during the heating cycles. Together with a developed software tool, which is suitable for calculation of the dynamical temperature distribution across the wafer under process conditions where the convective heat losses can be neglected, the influence of heating-up velocities is investigated. The obtained results show that in a scalar controlled system process conditions optimized for steady state lead to maximum temperature nonhomogeneity during the heating-up period, due to the changing heat balance in the system.
The goal in Rapid Thermal Processing is the realization of homogeneous and stable temperature distribution across the wafer.
Due to the wafer edge an additional heat loss occurs, which leads to temperature decrease near the wafer boundary. This can be the origin for layer thickness inhomogenities and defect generation. For successful compensation it is necessary to know why such a temperature gradient exists.
The heat transfer at the wafer edge was investigated by using computer simulation.
The results confirmed by experimental data in the pressure range of 1.. 760 Torr are discussed and criteria for the compensation of the temperature gradient near the wafer edge are developed.
The synthesis of nc-Si by reactive evaporation of SiO and subsequent thermal induced phase separation is reported. The size control of nc-Si is realized by evaporation of SiO/SiO2 superlattices. By this method an independent control of crystal size and density is possible. The phase separation of SiO into SiO2 and nc-Si in the limit of ultrathin layers is investigated. Different steps of this phase separation are characterized by photoluminescence, infrared absorption and transmission electron microscopy measurements. The strong room temperature luminescence of nc-Si shows a strong blueshift of the photoluminescence signal from 850 to 750 nm with decreasing crystal size. Several size dependent properties of this luminescence signal, like decreasing radiative lifetime and increasing no-phonon transition properties with decreasing crystal size are in good agreement with the quantum confinement model. Er doping of the nc-Si shows an enhancement of the Er luminescence at 1.54 μm by a factor of 5000 compared to doped SiO2 layers. The decreasing transfer time for the nc-Si to Er transition with decreasing crystal size can be understood as additional proof of increasing recombination probability within the nc-Si for decreasing crystal size.
Polymers are currently considered as a possible alternative to silicon dioxide in the fabrication of interlevel dielectrics. To penetrate mainstream semiconductor device fabrication polymers have to meet a number of requirements regarding their long-term stability. One aspect is the mechanical stability of integrated polymer films under changing climatic conditions. In the present work, the impact of ambient moisture on the mechanical properties of thin polymer films (PI, BCB, and PFCB) was investigated. The sorption of water molecules in these materials typically causes an anisotropic volume expansion, resulting in increased mechanical film stress if the film is physically constrained by adjacent inorganic structures. Especially polyimides show both considerable moisture uptake and large changes in the mechanical film stress, while BCB and PFCB are virtually insensitive to ambient moisture. In the paper, experimental data (water uptake, in-plane swelling, out-of-plane swelling) are presented and discussed in detail.
The interaction of ethene with silicon (111) surfaces at different process temperatures (580°C, 680°C, 780°C) was monitored in situ by spectroscopic ellipsometry. It is shown that spectroscopic ellipsometry is a reliable method to monitor the carbonization process of silicon surfaces. Different SiC formation stages (incubation time, (√3×√3)R30° reconstruction, 2D growth and 3D growth) were observed using complimentary analyzing techniques. The change of the ellipsometric signal as a function of process time is related to these stages and was interpreted using an optical model which consists of four layers (surface roughness, SiC layer, interface layer, Si substrate).
Au-ions were implanted at RT conventionally and through a mask into TiO2- and SrTiO3-single crystals with doses in the range from 1×1015Au+/cm2 to 1×1017Au+/cm2, and dose rates of ∼1011ions/sec and ∼3×1013ions/sec, at an energy of 260keV; some samples subsequently were annealed at temperatures up to 1100K. The Au-atoms precipitated to nanocrystals during implantation with an average particle size of 1.5nm. HRTEM investigations revealed that the Au-nanocrystals, embedded in amorphous TiO2-regions, have a broad size distribution varying from large sizes in the near surface region to smaller sizes at larger depths. In the annealing process a coarsening and a reorientation of the Au-nanocrystals is observed. At 1000K the particle size of the textured Au-implant was evaluated to be ∼6nm. Implantation with a high dose rate performed through a metal mask with holes of 120μm diameter and without annealing resulted in an almost equidistant arrangement of the Au-nanocrystals with a narrow size distribution of 2–6nm in TiO2 and 3–5nm in SrTiO3 in the near surface region. Au-ion implantation through an e-beam resist mask (50nm × 50nm holes), with doses ranging from 1×1015Au+/cm2 to 4×1015Au+/cm2 at the low dose rate and annealed at 1000K, lead to a periodic structure of the Au-nanocrystals. The nanocrystal size, evaluated from TEM analysis, in the as-implanted state was ∼5nm and after annealing at 1000K sizes of several nanometers to several tens of nanometers were observed.
This study uses various characterisation techniques on the razor shell (Ensis siliqua), to relate the shell's microstructure to its mechanical properties. Scanning electron microscopy (SEM) has shown that the outer and inner regions of the shell are composed of simple and complex crossed lamellar microstructures respectively. These layers are interspersed by prismatic layers of a completely different crystallographic orientation. Nanoindentation and microhardness measurements have shown that the structure is anisotropic, and Raman band shifts have been observed within these indented/deformed areas of shell, showing that the microstructure deforms rather than generating surface damage. The use of energy variable synchrotron X-ray diffraction has shown that the calcium carbonate crystals of the shell are preferentially orientated as a function of depth and that opposing residual stresses exist at the outer and inner regions of the shell. This study has analysed several microstructural features of the shell and provided an insight into how they prevent failure of the material.
The drive for greater use of renewable materials is one that has recently gained momentum due to the need to rely less heavily on petroleum. These renewable materials are defined as such since they are derived from plant-based sources. Some renewable materials also offer properties that conventional materials cannot provide: hierarchical structure, environmental compatibility, low thermal expansion, and the ability to be modified chemically to suit custom-made applications. Nature's materials, particularly from plant- and animal-based polysaccharides and proteins, have hierarchical structures, and these structures can be utilized for conventional applications via biomimetic approaches. This issue begins with an article covering renewable polymers or plastics that can be used to generate block copolymers (where two polymers with specific functions are combined) as an alternative to conventional materials. Applications of renewable polymers, such as cellulose from plants, bacteria, and animal sources, are also covered. Also presented are the use of bacterial cellulose and other plant-based nanofibers for transparent electronic display screens and, in a wider sense, the use of cellulose nanofibers for composite materials, where renewable resources are required to generate larger amounts of material. Finally, this issue shows the use of biomimetic approaches to take the multifunctional properties of renewable materials and use these concepts, or the materials themselves, in conventional materials applications.
The indentation properties of human fingernails at varying humidity are reported. The samples were indented using both microindentation, to obtain their Vickers hardness and also nanoindented using a Berkovich indenter tip. The relative humidity (RH) of the samples was controlled by using salt solutions with a sealed and enclosed environment surrounding the testing equipment. It was shown that the Vickers hardness of the samples is sensitive to RH, with recovery of the nail material more readily occurring for nails tested at >55% RH. This recovery mechanism is discussed in terms of the structure of the nails, and this approach is also suggested as a technique for following recovery mechanisms in natural materials under varying humidity. The hardness obtained by nanoindentation is similar to previously published data, but does not change with humidity. The modulus of the nails is also insensitive to relative humidity, but in the same range as the value derived from the microindentation tests.