Liquid chromatographic determination of aniline in table-top sweeteners based on pre-column derivatization with 1,2-naphthoquinone-4-sulfonate

A liquid chromatographic method for the determination of aniline in cyclamate sweeteners based on a pre-column derivatization with 1,2-naphthoquinone-4-sulfonate (NQS) is proposed. Aniline traces were extracted from the cyclamate samples using dichloromethane. After solvent evaporation, the dry residue was derivatized with NQS at pH 9.5 and 85 degrees C for 1 min. The aniline derivative, which was extracted from the reacting mixture, was redissolved in the eluent solution and injected into the chromatographic system. The separation of aniline derivative from other amine impurities was carried out in a C18 column using a 2% acetic acid-methanol (40:60, v/v) mobile phase. Results from the analysis of aniline in the sweetener samples with the proposed method were compared with those from the standard method. A good concordance between the two methods was observed.     

Determination of the metric from the curvature

A method of calculating the metric from the curvature is presented. Assuming that a tensor with the symmetry properties of a type D curvature tensor is given in an orthonormal tetrad, we use the Bianchi identities and the relationship between the connection and the tetrad in order to calculate, under certain assumptions, the corresponding metric. Some well-known metrics are derived from the curvature by using the method given here.     

Ferromagnetism in fcc twinned 2.4 nm size Pd nanoparticles

The onset of ferromagnetism has been experimentally observed in small Pd particles of average diameter 2.4 nm. High-resolution studies reveal that a high percentage of the fcc particle exhibits single and multiple twinning boundaries. The spontaneous magnetization close to 0.02 emu/g seems to indicate that only a small fraction of atoms holds a permanent magnetic moment and contributes to ferromagnetism. The possible origin of ferromagnetism is briefly discussed according to different models recently reported.     

Power-law-distributed dark states are the main pathway for photobleaching of single organic molecules

We exploit the strong excitonic coupling in a superradiant trimer molecule to distinguish between long-lived collective dark states and photobleaching events. The population and depopulation kinetics of the dark states in a single molecule follow power-law statistics over 5 orders of magnitude in time. This result is consistent with the formation of a radical unit via electron tunneling to a time-varying distribution of trapping sites in the surrounding polymer matrix. We furthermore demonstrate that this radicalization process forms the dominant pathway for molecular photobleaching.     

Towards the deformation quantization of linearized gravity

We present a first attempt to apply the approach of deformation quantization to linearized Einstein's equations. We use the analogy with Maxwell equations to derive the field equations of linearized gravity from a modified Maxwell Lagrangian which allows the construction of a Hamiltonian in the standard way. The deformation quantization procedure for free fields is applied to this Hamiltonian. As a result we obtain the complete set of quantum states and the discrete energy spectrum of linearized gravity.     

High-resolution magnetic imaging by local tunneling magnetoresistance

We give an overview over our recent efforts of high-resolution magnetic imaging using scanning tunneling microscopy with a ferromagnetic tip. Magnetic sensitivity is obtained on the basis of local tunneling magnetoresistance between a soft magnetic tip and the sample. The magnetisation of the tip is switched periodically with a small coil, leading to variations of the tunneling current due to the tunneling magnetoresistance effect. These variations are detected with a lock-in amplifier to separate spin-dependent parts from the topographic parts of the tunneling current such that the topography and the magnetic structure of the sample can be recorded simultaneously. Crucial for this method is to avoid mechanical vibrations of the tip, that may also lead to variations in the tunneling current. Exemplary studies of polycrystalline Ni and the closure domain pattern of Co(0001) are presented, showing high contrast at acquisition times as low as 3 ms/pixel and a lateral resolution of the order of 1 nm. Further it is demonstrated that besides topography and magnetisation, also local information about the magnetic susceptibility can be obtained. Received: 28 April 2000 / Accepted: 15 May 2000 / Published online: 7 March 2001     

Magnetization reversal asymmetry in Fe/MgO(0 0 1) thin films

We study the in-plane magnetization process in 200 Å Fe(0 0 1) thin films grown by sputtering at normal incidence. In spite of this growth geometry, a small uniaxial in plane magnetic anisotropy, whose origin is not totally understood, is found superimposed to the expected cubic biaxial one. This has a dramatic effect both on the reversal process and the domain structure. A combined longitudinal and transversal Kerr study shows the different switching processes (180° walls along the main easy axis versus 90° along the secondary easy axis) depending on the relative orientation of the magnetic field with respect to the Fe crystallographic axes. Remarkably, this two- and sometimes three-step switching process appears only when the field is applied along certain crystallographic directions. These findings are corroborated by domain observations.