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- ItemPolymeric monolithic materials: Syntheses, properties, functionalization and applications(Amsterdam : Elsevier, 2007) Buchmeiser, M.R.The synthetic particularities for the synthesis of polymer-based monolithic materials are summarized. In this context, monoliths prepared via thermal-, UV- or electron-beam triggered free radical polymerization, controlled TEMPO-mediated radical polymerization, polyaddition, polycondensation as well as living ring-opening metathesis polymerization (ROMP) will be covered. Particular attention is devoted to the aspects of controlling pore sizes, pore volumes and pore size distributions as well as functionalization of these supports. Finally, selected, recent applications in separation science, (bio-) catalysis and chip technology will be summarized. © 2007 Elsevier Ltd. All rights reserved.
- ItemInvestigation of changes in crystalline and amorphous structure during deformation of nano-reinforced semi-crystalline polymers by space-resolved synchrotron saxs and waxs(Amsterdam : Elsevier, 2009) Schneider, K.; Schone, A.; Jun, T.-S.; Korsunsky, A.M.Complex structural changes occur in semi-crystalline polymers during deformation. In (nano-)filled systems the situation becomes even more complicated, since not only phase changes may take place, but also local (interfacial) failure between phases may occur. To help identify specific processes taking place within these systems, simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS) measurements were performed using synchrotron radiation during in situ deformation. Using a highly focused beam, spatially resolved local information can be extracted by scanning the beam across the deformed/damaged region within the sample. The characteristic changes in the different phases are presented and discussed. While the study of WAXS patterns gives insight into the orientation and dimensions of the crystallites, SAXS provides information about the mutual arrangement of phases and the interfacial failure phenomena. Based on the analysis of the results obtained in our experiments it will be shown that the first changes in the crystalline phase appear long before macroscopic yielding of the sample is reached, i.e. the onset of irreversible deformation takes place. In the post-yield regime radical changes are observed in both the long- and short-range structures. It is concluded that the presence of nano-fillers exerts a strong influence on the establishment of microcrystalline structure, and hence also on the deformation behaviour at the microscopic scale.
- ItemElectronic structure and aspects of unconventional superconductivity in NaxCoO2.yH2O(São Carlos : Universidade Federal de São Carlos, 2003) Rosner, H.; Drechsler, S.-L.; Fuchs, G.; Handstein, A.; Wälte, A.; Müller, K.-H.We examine the electronic structure of NaxCoO2.yH2O within the local density approximation. The parametrization of the band which forms the largest hole-Fermi surface centered at G shows significant deviations from what is frequently assumed in recent sophisticated theoretical studies. In particular, the commonly used nearest neighbor approaches in the framework of single band pictures are found to be unrealistic. The special role of H2O in screening the disorder in the charge reservoir is briefly discussed and compared with the case of Y1–xCaxCu3O6+d.
- ItemFormation of star-like and core-shell AuAg nanoparticles during two- and three-step preparation in batch and in microfluidic systems(New York : Hindawi, 2007) Köhler, J.M.; Romanus, H.; Hübner, U.; Wagner, J.Regular dendrit-like metal nanoparticles and core-shell nanoparticles were formed by the reduction of mixtures of tetrachloroaurate and silver nitrate solutions with ascorbic acid at room temperature in two- and three-step procedures. The formation of these particles was found in batch experiments as well as in micro flow-through processes using static micromixers. The characteristic diameters of 4-branched star particles were in the range between 60 and 100 nm. The typical particles consist of four metal cores which are embedded in a common shell. Additionally, particles with five and more metallic cores were formed, to some extent, and aggregates of the 4-branched particles also were formed. Larger aggregates and network-like structures of connected star particles were formed after sedimentation. The properties of the formed particles are dependent on the educt concentrations as well as on the order of mixing steps and on the time interval between them. Obviously, the relation of nucleation and particle growth in relation to the concentrations of metal ions determines the composition and the properties of formed nanoparticles. So, star-like particles are observed in case of nucleation of Au in absence of silver ions but with silver deposition after short nucleation time. Spherical core shell particles are formed in case of silver salt addition after complete reduction of tetrachloroaurate in flow-through experiments with sufficient residence time between both mixing steps. Polymer layers are always found in the form of a second outer shell even if the polymer solutions are added in an early stage of particle formation.
- ItemArrays of regenerated fiber bragg gratings in non-hydrogen-loaded photosensitive fibers for high-temperature sensor networks(Basel : MDPI, 2009) Lindner, E.; Chojetztki, C.; Brueckner, S.; Becker, M.; Rothhardt, M.; Vlekken, J.; Bartelt, H.We report about the possibility of using regenerated fiber Bragg gratings generated in photosensitive fibers without applying hydrogen loading for high temperature sensor networks. We use a thermally induced regenerative process which leads to a secondary increase in grating reflectivity. This refractive index modification has shown to become more stable after the regeneration up to temperatures of 600 °C. With the use of an interferometric writing technique, it is possible also to generate arrays of regenerated fiber Bragg gratings for sensor networks. © 2009 by the authors.
- ItemIncreased biocompatibility and bioactivity after energetic PVD surface treatments(Basel : MDPI, 2009) Mändl, S.Ion implantation, a common technology in semiconductor processing, has been applied to biomaterials since the 1960s. Using energetic ion bombardment, a general term which includes conventional ion implantation plasma immersion ion implantation (PIII) and ion beam assisted thin film deposition, functionalization of surfaces is possible. By varying and adjusting the process parameters, several surface properties can be attuned simultaneously. Extensive research details improvements in the biocompatibility, mainly by reducing corrosion rates and increasing wear resistance after surface modification. Recently, enhanced bioactivity strongly correlated with the surface topography and less with the surface chemistry has been reported, with an increased roughness on the nanometer scale induced by self-organisation processes during ion bombardment leading to faster cellular adhesion processes. © 2009 by the authors;.
- ItemAn X-Band low-power and low-phase-noise VCO using bondwire inductor(München : European Geopyhsical Union, 2009) Hu, K.; Herzel, F.; Scheytt, J.C.In this paper a low-power low-phase-noise voltage-controlled-oscillator (VCO) has been designed and, fabricated in 0.25 μm SiGe BiCMOS process. The resonator of the VCO is implemented with on-chip MIM capacitors and a single aluminum bondwire. A tail current filter is realized to suppress flicker noise up-conversion. The measured phase noise is −126.6 dBc/Hz at 1 MHz offset from a 7.8 GHz carrier. The figure of merit (FOM) of the VCO is −192.5 dBc/Hz and the VCO core consumes 4 mA from a 3.3 V power supply. To the best of our knowledge, this is the best FOM and the lowest phase noise for bondwire VCOs in the X-band. This VCO will be used for satellite communications.
- ItemMagnetic field effects of double-walled carbon nanotubes(São Carlos : Universidade Federal de São Carlos, 2006) Latgé, A.; Grimm, D.; Ferreira, M.S.A theoretical discussion of electronic and transport properties of a particular family of double-wall carbon nanotubes, named commensurate structures of the armchair type (n,n)@(2n,2n) is addressed. A single p-band tight binding hamiltonian is considered and the magnetic field is theoretically described by following the Peierls approximation into the hopping energies. Our emphasis is put on investigating the main effects of the geometrical aspects and relative positions of the tubes on the local density of states and on the conductance of the system. By considering intershell interactions between a set of neighboring atoms on the walls of the inner and outer tubes, we study the possibility of founding Aharonov-Bohm effects in the DWCNs when a magnetic field is applied along the axial direction.
- ItemAdvances for the topographic characterisation of SMC materials(Basel : MDPI, 2009) Calvimontes, A.; Grundke, K.; Müller, A.; Stamm, M.For a comprehensive study of Sheet Moulding Compound (SMC) surfaces, topographical data obtained by a contact-free optical method (chromatic aberration confocal imaging) were systematically acquired to characterise these surfaces with regard to their statistical, functional and volumetrical properties. Optimal sampling conditions (cut-off length and resolution) were obtained by a topographical-statistical procedure proposed in the present work. By using different length scales specific morphologies due to the influence of moulding conditions, metallic mould topography, glass fibre content and glass fibre orientation can be characterized. The aim of this study is to suggest a systematic topographical characterization procedure for composite materials in order to study and recognize the influence of production conditions on their surface quality. © 2009 by the authors.
- ItemRemote system for detection of low-levels of methane based on photonic crystal fibres and wavelength modulation spectroscopy(New York, NY : Hindawi, 2009) Carvalho, J.P.; Lehmann, H.; Bartelt, H.; Magalhes, F.; Amezcua-Correa, R.; Santos, J.L.; Roosbroeck, J.V.; Arajo, F.M.; Ferreira, L.A.; Knight, J.C.In this work we described an optical fibre sensing system for detecting low levels of methane. The properties of hollow-core photonic crystal fibres are explored to have a sensing head with favourable characteristics for gas sensing, particularly in what concerns intrinsic readout sensitivity and gas diffusion time in the sensing structure. The sensor interrogation was performed applying the Wavelength Modulation Spectroscopy technique, and a portable measurement unit was developed with performance suitable for remote detection of low levels of methane. This portable system has the capacity to simultaneously interrogate four remote photonic crystal fibre sensing heads. Copyright © 2009 J. P. Carvalho et al.