We investigated the magnetic properties of ultrathin magnetite films deposited directly on MgO(001) and on a Fe(001) buffer layer. In both cases the magnetite surface structure could be identified using low energy ele...
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We investigated the magnetic properties of ultrathin magnetite films deposited directly on MgO(001) and on a Fe(001) buffer layer. In both cases the magnetite surface structure could be identified using low energy electron diffraction. The conversion electron Mössbauer spectroscopy measurements proved that, for magnetite films deposited on the Fe buffer, superparamagnetic relaxation was strongly suppressed. The effect of a Fe overlayer on the magnetite film grown directly on MgO is considerably weaker. Longitudinal Kerr magnetometry indicated the presence of the ferromagnetic interfacial coupling between Fe and magnetite films. We conclude that the density of antiphase boundaries for films grown on the Fe buffer is lower than that of Fe 3O4/MgO films.
The access to x-rays of third generation synchrotron radiation sources enables studies of dynamics in metallic systems. The nuclear resonant scattering (NRS) method provides information about elementary atomic jumps. ...
The access to x-rays of third generation synchrotron radiation sources enables studies of dynamics in metallic systems. The nuclear resonant scattering (NRS) method provides information about elementary atomic jumps. When used in grazing incidence geometry, the sensitivity of the NRS method can be tuned to the surface region. This makes the method especially useful for thin film investigations. Contrary to other surface sensitive methods this technique is not only limited to the surface itself: it allows to retrieve the depth profile of diffusivity from the surface down to the bulk region of the measured sample. Fe-Si intermetallic films with a D03 structure and close to the stoichiometric Fe3Si composition have been prepared on an MgO (100) substrate. The NRS measurements in grazing incidence geometry yielded maximum iron diffusivity at the surface and diminishing continuously with the depth. The depth and temperature dependence have been measured and compared with the bulk values.
In this paper we show that series-parallel graphs (i.e., K 4-minor free graphs) can be represented as contact intersection graphs of straight-line segments in three directions. Moreover, in our representations no two ...
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ISBN:
(纸本)1860948278
In this paper we show that series-parallel graphs (i.e., K 4-minor free graphs) can be represented as contact intersection graphs of straight-line segments in three directions. Moreover, in our representations no two segments of the same direction intersect.
The non‐existence of uncharged black holes and charged black holes in the Maxwell electrodynamics, with non‐trivial scalar field has been proved for a large class of scalar‐tensor theories. The no‐scalar‐hair the...
The non‐existence of uncharged black holes and charged black holes in the Maxwell electrodynamics, with non‐trivial scalar field has been proved for a large class of scalar‐tensor theories. The no‐scalar‐hair theorems, however, do not apply in the case of non‐linear electrodynamics. In the present work numerical solutions describing charged black holes coupled to Euler‐Heisenberg type non‐linear electrodynamics in scalar‐tensor theories of gravity with massless scalar field are found. The causal structure and properties of the solutions are studied, and a comparison between these solutions and the corresponding solutions in the General relativity is made.
We describe a method for the construction of specific types of neural networks composed of structures directly linked to the structure of the molecule under consideration. Each molecule can be represented by a unique ...
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We describe a method for the construction of specific types of neural networks composed of structures directly linked to the structure of the molecule under consideration. Each molecule can be represented by a unique neural connectivity problem (graph) which can be programmed onto a cellular neural network. A composite network can further successfully perform classification and regression on real-world chemical data sets. The method can be regarded as a statistical learning procedure that turns the molecular graph, representing the 2D formula of the compound, into an adaptive whole molecule composite descriptor. By translating the molecular graph structure into a dynamical system, the algorithm can compute an output value that is highly sensitive to the molecular topology. This system can be trained by gradient descent techniques which rely on the efficient calculation of the gradient by backpropagation.
Grazing-Incidence Small Angle X-ray Scattering (GISAXS) and X-Ray Photon Correlation Spectroscopy (XPCS) studies of island growth in two different systems are presented: 5 ML of iron on MgO(001) and 10 ML of iron on A...
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Grazing-Incidence Small Angle X-ray Scattering (GISAXS) and X-Ray Photon Correlation Spectroscopy (XPCS) studies of island growth in two different systems are presented: 5 ML of iron on MgO(001) and 10 ML of iron on Au(001). Due to a missing conducting surface Fe/MgO thinner than approximately 20 ML could not be studied previously by common methods like STM. Fe/Au(001) is interesting as atoms of gold diffuse easily through iron layers and form precipitates. The coarsening dynamics of these precipitates is investigated by XPCS in GISAXS geometry. Their growth depends on the crystallographic directions of the substrate and correlates with the morphology measured by STM microscopy. Measurements were performed at the ESRF in Grenoble.
For a new generation of 2-D neutron detectors developed in the framework of the EU NMI3 project DETNI [1], the 128-channel frontend chip n-XYTER has been designed. To facilitate the reconstruction of single neutron in...
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ISBN:
(纸本)9789290832881
For a new generation of 2-D neutron detectors developed in the framework of the EU NMI3 project DETNI [1], the 128-channel frontend chip n-XYTER has been designed. To facilitate the reconstruction of single neutron incidence points, the chip has to provide a spatial coordinate (represented by the channel number), as well as time stamp and amplitude information to match the data of x-and y-coordinates. While the random nature of the input signals calls for self-triggered operation of the chip, on-chip derandomisation and sparsification is required to exploit the enormous rate capability of these detectors (≥ 4 × 106cm-2s-1). The chosen architecture implements a preamplifier driving two shapers with different time constants per channel. The faster shaper drives a single-pulse discriminator with subsequent time-walk compensation. The output of this circuit is used to latch a 14-bit time stamp with a ≤ 2 ns resolution and to enable a peak detector circuit fed by the slower shaper branch. The analogue output of the peak detector as well as the time stamp are stored in a 4-stage FIFO for derandomisation. The readout of these FIFOs is accomplished by a token-ring based multiplexer working at 32 MHz, which accounts for further derandomisation, sparsification and dynamic bandwidth distribution. The chip was submitted for manufacturing in AMS's C35B4M3 0.35μm CMOS technology in June 2006.
We study an electron-hole pair in laterally coupled self-assembled quantum dots with an electric field applied in the plane of confinement. The interparticle correlations and the carrier distribution are calculated us...
We study an electron-hole pair in laterally coupled self-assembled quantum dots with an electric field applied in the plane of confinement. The interparticle correlations and the carrier distribution are calculated using a configuration interaction approach for dots with circular and square symmetry. We extract universal features of the photoluminescence spectra specific to the lateral coupling configuration and point out the differences with vertically coupled dots. These specific features include additional avoided crossings of the lowest bright exciton level as function of the external field. In the case of strong coupling, the avoided crossing related to exciton dissociation is anomalous and involves an interaction of three or four energy levels. The latter is a consequence of the hole state mixing appearing at the electron transfer between the dots.
In the present, work we find new non-unique, numerical solutions describing charged black holes coupled to non-linear electrodynamics in a special type of scalar-tensor theory. The solutions describe three phases of b...
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We study the effect of an electric field on an electron-hole pair in an asymmetric system of vertically coupled self-assembled quantum dots taking into account their nonperfect alignment. We show that the nonperfect a...
We study the effect of an electric field on an electron-hole pair in an asymmetric system of vertically coupled self-assembled quantum dots taking into account their nonperfect alignment. We show that the nonperfect alignment does not qualitatively influence the exciton Stark effect for the electric field applied in the growth direction, but can be detected by application of a perpendicular electric field. We demonstrate that the direction of the shift between the axes of nonaligned dots can be detected by rotation of a weak electric field within the plane of confinement. Already for a nearly perfect alignment the two-lowest energy bright exciton states possess antilocked extrema as a function of the orientation angle of the horizontal field which appear when the field is parallel to the direction of the shift between the dot centers.
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