236 research outputs found

    Optical Position and Time Resolved Measurement of Magnetic Field Distribution in High Speed Metal Forming

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    In the area of the position and time resolved measurement of the magnetic field distribution in small gaps between workpieces and coils in high-speed sheet metal forming optical sensors are predestined to be integrated into the very small geometries of experimental setups. Optical sensors for current measurement based on the magneto-optic Faraday effect are well known for a long time. This effect can also be used for the direct measurement of magnetic fields. For the use in electromagnetic high-speed metal forming applications, only very small field probes are probable. The measurement of axial symmetric fields can be achieved with two connected fibres with different Verdet constants. They solve the problem with the not given measurement value, which occurs by the use of only one fibre because of its closed integral domain. A continuous time signal of the magnetic field can be calculated for discrete regions. Likewise, it is possible to employ miniature fibre-optic magnetic field point sensors for the field determination in the gap of an electromagnetic high-speed forming device. It is necessary to examine the influence on the polarisation state and the intensity of the light in a fibre. There are two different sensors shown in this paper. One is based on a piece of flint glass fibre spliced between two polarising fibres, and the other sensor arrangement consists of two glued SiO_2 blocks. A workbench for assembling of fibre-optic sensors using the splice technology has been constructed and will be presented. First trial measurements of the magnetic field, compared to the causing current, show the functionality of these kinds of optical sensors and are discussed under the aspect of optimisation

    Development and test of a planar R-band accelerating structure

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    Planar accelerating structures, so called muffin tins, are of great interest for new accelerating techniques which are operating at high frequencies. At present the upper frequency limit for high power sources is 29.9855 GHz available at CERN. Therefore a new design of a planar traveling wave constant impedance accelerating structure is presented. A fully engineered 37-cell prototype with an operating frequency of 29.9855 GHz, which is designed for the 2 pi /3-mode, was fabricated by CNC milling technology. The design includes a power coupler, a cavity geometry optimized to compensate the effect of transverse forces, vacuum flanges and beam pipe flanges. Shown are the frequency scan of transmission and reflection measurements compared to numerical simulations with GdfidL. Further, a non resonant bead pull measurement was made to determine and verify the fundamental modes of the structure. The cavity is planned to be powered at the CLIC test stand at CERN. (4 refs)

    Transient pool boiling in microgravity

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    Transient nucleate pool boiling experiments using R113 are conducted for short times in microgravity and in earth gravity with different heater surface orientations and subcoolings. The heating surface is a transparent gold film sputtered on a quartz substrate, which simultaneously provides surface temperature measurements and permits viewing of the boiling process from beneath. For the microgravity experiments, which have uniform initial temperatures and no fluid motion, the temperature distribution in the R113 at the moment of boiling inception is known. High speed cameras with views both across and through the heating surface record the boiling spread across the heater surface, which are classified into six (6) distinct categories.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30197/1/0000585.pd

    Strain dependent light-off temperature in catalysis revealed by planar laser-induced fluorescence

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    Understanding how specific atom sites on metal surfaces lower the energy barrier for chemical reactions is vital in catalysis. Studies on simplified model systems have shown that atoms arranged as steps on the surface play an important role in catalytic reactions, but a direct comparison of how the light-off temperature is affected by the atom orientation on the step has not yet been possible due to methodological constraints. Here we report in situ spatially resolved measurements of the CO production over a cylindrical-shaped Pd catalyst and show that the light-off temperature at different parts of the crystal depends on the step orientation of the two types of steps (named A and B). Our finding is supported by density functional theory calculations, revealing that the steps, in contrast to what has been previously reported in the literature, are not directly involved in the reaction onset but have the role of releasing stress.The authors thank the Knut and Alice Wallenberg Foundation, the Swedish Research Council, the Swedish Foundation for Strategic Research, and the Crafoord Foundation. Support by the MAX IV staff is gratefully acknowledged. The calculations were performed at C3SE through a SNIC grant. J.E.O. acknowledges support from the Spanish Ministry of Economy (MAT2013-46593-C6-4-P) and the Basque Government (IT621-13).Peer Reviewe

    Steps and catalytic reactions: CO oxidation with preadsorbed O on Rh(553)

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    Industrial catalysts are often comprised of nanoparticles supported on high-surface-area oxides, in order to maximise the catalytically active surface area and thereby utilise the active material better. These nanoparticles expose steps and corners that, due to low coordination to neighboring atoms, are more reactive and, as a consequence, are often assumed to have higher catalytic activity. We have investigated the reaction between CO and preadsorbed O on a stepped Rh(553) surface, and show that CO oxidation indeed occurs faster than on the flat Rh(111) surface at the same temperature. However, we do find that this is not a result of reactions at the step sites but rather at the terrace sites close to the steps, due to in-plane relaxation enabled by the step. This insight can provide ways to optimize the shape of the nanoparticles to further improve the activity of certain reactions

    The effect of different In2_2O3_3(111) surface terminations on CO2_2 adsorption

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    In2_2O3_3-based catalysts have shown high activity and selectivity for CO2_2 hydrogenation to methanol, however the origin of the high performance of In2_2O3_3 is still unclear. To elucidate the initial steps of CO2_2 hydrogenation over In2_2O3_3, we have combined X-ray Photoelectron Spectroscopy (XPS) and Density Functional Theory (DFT) calculations to study the adsorption of CO2_2 on the In2_2O3_3(111) crystalline surface with different terminations, namely the stoichiometric, the reduced, and the hydroxylated surface, respectively. The combined approach confirms that the reduction of the surface results in the formation of In ad-atoms and that water dissociates on the surface at room temperature. A comparison of the experimental spectra and the computed core-level-shifts (using methanol and formic acid as benchmark molecules) suggests that CO2_2 adsorbs as a carbonate on all surface terminations. We find that CO2_2 adsorption is hindered by hydroxyl groups on the hydroxylated surface.Comment: 49 pages, 18 figure

    A Forward Genetic Screen in Mice Identifies Mutants with Abnormal Cortical Patterning

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    Formation of a 6-layered cortical plate and axon tract patterning are key features of cerebral cortex development. Abnormalities of these processes may be the underlying cause for a range of functional disabilities seen in human neurodevelopmental disorders. To identify mouse mutants with defects in cortical lamination or corticofugal axon guidance, N-ethyl-N-nitrosourea (ENU) mutagenesis was performed using mice expressing LacZ reporter genes in layers II/III and V of the cortex (Rgs4-lacZ) or in corticofugal axons (TAG1-tau-lacZ). Four lines with abnormal cortical lamination have been identified. One of these was a splice site mutation in reelin (Reln) that results in a premature stop codon and the truncation of the C-terminal region (CTR) domain of reelin. Interestingly, this novel allele of Reln did not display cerebellar malformation or ataxia, and this is the first report of a Reln mutant without a cerebellar defect. Four lines with abnormal cortical axon development were also identified, one of which was found by whole-genome resequencing to carry a mutation in Lrp2. These findings demonstrated that the application of ENU mutagenesis to mice carrying transgenic reporters marking cortical anatomy is a sensitive and specific method to identify mutations that disrupt patterning of the developing brain

    Structure of the SnO2(110)-(4 x 1) Surface

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    Using surface x-ray diffraction (SXRD), quantitative low-energy electron diffraction (LEED), and density-functional theory (DFT) calculations, we have determined the structure of the (4 × 1) reconstruction formed by sputtering and annealing of the SnO2ð110Þ surface. We find that the reconstruction consists of an ordered arrangement of Sn3O3 clusters bound atop the bulk-terminated SnO2ð110Þ surface. The model was found by application of a DFT-based evolutionary algorithm with surface compositions based on SXRD, and shows excellent agreement with LEED and with previously published scanning tunneling microscopy measurements. The model proposed previously consisting of inplane oxygen vacancies is thus shown to be incorrect, and our result suggests instead that Sn(II) species in interstitial positions are the more relevant features of reduced SnO2ð110Þ surfaces
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