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71.
Alexander Kassler Ernst Pittenauer Nicole Doerr Guenter Allmaier 《Rapid communications in mass spectrometry : RCM》2009,23(24):3917-3927
The aim of this study was to investigate the utility of ion trap mass spectrometry (ITMS) in combination with the two desorption/ionization methods, electrospray (ESI) and atmospheric pressure matrix‐assisted laser desorption/ionization (AP‐MALDI), for the detection of antioxidants which are applied in lubricants. These experiments should form the base for future investigations of antioxidants in tribologically formed thin layers on the surface of frictional systems. Seventeen different antioxidants were selected out of the group of hindered phenolic and aromatic aminic compounds. Practically all antioxidants could be characterized by positive ion ESI‐ and AP‐MALDI‐ITMS, forming various types/species of molecular ions (e.g. [M]+ . , [M+H]+, [M+Na]+ or [M–2H+H]+). A few compounds could be analyzed by negative ion ESI‐MS, too, but none by negative ion AP‐MALDI‐MS. The influence of target materials in AP‐MALDI‐MS (gold‐ and titanium nitride (TiN)‐covered stainless steel, micro‐diamond‐covered hard metal, hand‐polished and sand‐blasted stainless steel targets) with respect to the molecular ion intensity and type of molecular ion of two selected antioxidants was evaluated. The surface properties are of particular interest because in friction tests different materials with different surface characteristics are used. However, the MS results indicate that optimal target surfaces have to be found for individual antioxidants in AP‐MALDI‐MS but in general smooth surfaces were superior to rough surfaces. Finally the gold‐covered stainless steel MALDI target provided the best mass spectra and was selected for all the antioxidants investigated. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
72.
S. Kramp M. Doerr M. Rotter M. Loewenhaupt R. v.d. Kamp 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):559-563
The magnetic (H
,
T)-phase diagram of the orthorhombic compound NdCu2 was investigated for external magnetic fields up to 15 T parallel to the crystallographic c-direction. Magnetization and magnetostriction measurements reveal an anomalous change of the magnetic properties as well
as giant magnetostriction (GMS) and large hysteretic effects. This behaviour is similar to that observed in some other RCu2 compounds where it has been interpreted as a conversion of the magnetic Ising axis. In contrast to these other RCu2 compounds, however, the easy axis of magnetization in NdCu2 is the b-axis. The macroscopic measurements are compared with neutron diffraction experiments which reveal GMS along the b-axis and a new magnetic phase with propagation vector in the converted crystal.
Received 27 March 2000 and Received in final form 11 September 2000 相似文献
73.
M. Doerr S. Raasch M. Rotter M. Frontzek D. C. Meyer T. Leisegang M. Zschintzsch P. Svoboda M. Loewenhaupt 《The European physical journal. Special topics》2008,158(1):125-130
The volume, shape and microstructure of solids can be influenced by magnetic fields. Much effort is focused on magnetic shape
memory (MSM) materials. Recently, the MSM effect has been discovered to occur also in the paramagnetic state, e.g. in RCu2 compounds (R = rare earth). RMSM materials distinguish themselves from conventional MSM materials by the new origin of the
magnetoic anisotropy: the strong rare-earth single ion anisotropy. Due to the pseudo-hexagonal symmetry of RCu2, three orientational variants exists, each of them rotated by about 60 deg with respect to the others. Switching these variants
by an external field results in a change of the macroscopic shape. The strain is in the order of one percent (= Giant MagnetoStrain).
The variant's fraction remains unchanged when ramping down the field. The virgin state can be recovered by heating or by a
perpendicularly directed field. We present temperature and field dependent measurements of magnetostrain and magentization
at the model substance Tb0.5Dy0.5Cu2. The macroscopic characterization of the sample is complemented by a detailed microscopic analysis done by elastic neutron
scattering. Although the GMS effect of RCu2 was worked out at single crystals, the principle of this magneto-mechanical coupling phenomenon is also useful for polycrystalline
or microscaled applications. The existence of this structural irreversibility shows the potential to construct field controlled
actuators or switches. 相似文献
74.
Beyond Constructivism 总被引:1,自引:0,他引:1
75.
Monika Doerr Ingo Lüderwald Hans -Rolf Schulten 《Fresenius' Journal of Analytical Chemistry》1984,318(5):339-342
Summary Field desorption and fast atom bombardment mass spectrometry in the positive and negative modes have been applied to characterize poly(ethyleneadipate). Diagnostic ions up to the mass range of 1,400 have been found which allow elucidation of the degradation pathways of the polymer and its identification.
Charakterisierung von Polymeren durch Felddesorption- und Fast Atom Bombardment-Massenspektrometrie
Zusammenfassung Felddesorption- und Fast Atom Bombardment-Massenspektrometrie mit positiver und negativer Registrierung wurden für die Charakterisierung von Poly(ethylenadipat) eingesetzt. Diagnostische Ionensignale bis zur Masse 1400 wurden gefunden und ermöglichen die Kennzeichnung der Abbauwege des Polymers sowie seine Identifizierung,相似文献
76.
The antiferromagnet GdAg2 has been shown to be a good model system for the magnetoelastic paradox (MEP), because it exhibits large symmetry conserving magnetoelastic strains and the antiferromagnetic propagation vector breaks the tetragonal lattice symmetry (therefore a large symmetry breaking magnetoelastic strain can be expected in a single magnetic structure). As in many similar Gd based compounds no symmetry breaking strain has been found in the experiment. In order to investigate this MEP further, we have measured magnetostriction and magnetization on a textured polycrystal. The behaviour closely resembles that of GdNi2B2C, the prototype system for the magnetoelastic paradox (MEP). Our forced magnetostriction data indicate that the crystal distorts in applied magnetic field and gives further evidence that the MEP is a low field effect. The observed phase transitions are in agreement with available specific heat and neutron diffraction data. Moreover, the saturation magnetic field was measured in high pulsed magnetic fields and agrees well with the value calculated from the Standard Model of Rare Earth Magnetism (SMREM). 相似文献
77.
78.
79.
80.
Joshua Cooper Benjamin Doerr Joel Spencer Gbor Tardos 《European Journal of Combinatorics》2007,28(8):2072
Jim Propp’s P-machine, also known as the ‘rotor router model’, is a simple deterministic process that simulates a random walk on a graph. Instead of distributing chips to randomly chosen neighbors, it serves the neighbors in a fixed order.We investigate how well this process simulates a random walk. For the graph being the infinite path, we show that, independent of the starting configuration, at each time and on each vertex, the number of chips on this vertex deviates from the expected number of chips in the random walk model by at most a constant c1, which is approximately 2.29. For intervals of length L, this improves to a difference of O(logL), for the L2 average of a contiguous set of intervals even to . All these bounds are tight. 相似文献