266 research outputs found
Preparation and characterization of X ray mirrors with three single layers of a C, B4C and Ni onto two 820 mm long Si substrate
Optimization of Material Contrast for Efficient FIBâSEM Tomography of Solid Oxide Fuel Cells
Focused ion beam (FIB) â scanning electron microscopy (SEM) serial sectioning tomography has become an important tool for threeâdimensional microstructure reconstruction of solid oxide fuel cells (SOFC) to obtain an understanding of fabricationârelated effects and SOFC performance. By sequential FIB milling and SEM imaging a stack of crossâsection images across all functional SOFC layers was generated covering a large volume of 3.5·10 ÎŒm. One crucial step is image segmentation where regions with different image intensities are assigned to different material phases within the SOFC. To analyze all relevant SOFC materials, it was up to now mandatory to acquire several images by scanning the same region with different imaging parameters because sufficient material contrast could otherwise not be achieved. In this work we obtained highâcontast SEM images from a single scan to reconstract all functional SOFC layers consisting of a Ni/YOâdoped ZrO (YDZ) cermet anode, YDZ electrolyte and (La,Sr)MnO/YDZ cathode. This was possible by using different, simultaneous readâout detectors installed in a stateâofâtheâart scanning electron microscope. In addition, we used a deterministic approach for the optimization of imaging parameters by employing Monte Carlo simulations rather than trialâandâerror tests. We also studied the effect of detection geometry, detecting angle range and detector type
Barycentric decomposition of quantum measurements in finite dimensions
We analyze the convex structure of the set of positive operator valued
measures (POVMs) representing quantum measurements on a given finite
dimensional quantum system, with outcomes in a given locally compact Hausdorff
space. The extreme points of the convex set are operator valued measures
concentrated on a finite set of k \le d^2 points of the outcome space, d<
\infty being the dimension of the Hilbert space. We prove that for second
countable outcome spaces any POVM admits a Choquet representation as the
barycenter of the set of extreme points with respect to a suitable probability
measure. In the general case, Krein-Milman theorem is invoked to represent
POVMs as barycenters of a certain set of POVMs concentrated on k \le d^2 points
of the outcome space.Comment: !5 pages, no figure
Permafrost degradation at two monitored palsa mires in north-west Finland
Palsas and peat plateaus are expected to disappear from many regions, including Finnish Lapland. However, detailed long-term monitoring data of the degradation process on palsas are scarce. Here, we present the results of the aerial photography time series analysis (1959â2021), annual real-time kinematic (RTK) GNSS and active layer monitoring (2007â2021), and annual unoccupied aerial system surveys (2016â2021) at two palsa sites (Peera and Laassaniemi, 68ââN) located in north-west Finland. We analysed temporal trends of palsa degradation and their relation to climate using linear regression. At both sites, the decrease in palsa area by â77â% to â90â% since 1959 and height by â16â% to â49â% since 2007 indicate substantial permafrost degradation throughout the study periods. The area loss rates are mainly connected to winter air temperature changes at Peera and winter precipitation changes at Laassaniemi. The active layer thickness (ALT) has varied annually between 2007 and 2021 with no significant trend and is related mainly to the number of very warm days during summer, autumn rainfall of previous year, and snow depths at Peera. At Laassaniemi, the ALT is weakly related to climate and has been decreasing in the middle part of the palsa during the past 8 years despite the continuous decrease in palsa volume. Our findings imply that the ALT in the inner parts of palsas do not necessarily reflect the overall permafrost conditions and underline the importance of surface position monitoring alongside the active layer measurements. The results also showed a negative relationship between the ALT and snow cover onset, indicating the complexity of climateâpermafrost feedbacks in palsa mires.</p
Effect of Yttrium (Y) and Zirconium (Zr) Doping on the Thermodynamical Stability of the Cubic Ba<sub>0.5</sub>Sr<sub>0.5</sub>Co<sub>0.8</sub>Fe0.2O<sub>3-ÎŽ</sub> Phase
Variation of elastic scattering across a quantum well
The Drude scattering times of electrons in two subbands of a parabolic
quantum well have been studied at constant electron sheet density and different
positions of the electron distribution along the growth direction. The
scattering times obtained by magnetotransport measurements decrease as the
electrons are displaced towards the well edges, although the lowest-subband
density increases. By comparing the measurements with calculations of the
scattering times of a two-subband system, new information on the location of
the relevant scatterers and the anisotropy of intersubband scattering is
obtained. It is found that the scattering time of electrons in the lower
subband depends sensitively on the position of the scatterers, which also
explains the measured dependence of the scattering on the carrier density. The
measurements indicate segregation of scatterers from the substrate side towards
the quantum well during growth.Comment: 4 pages, 4 figure
Unraveling the effect of ZrO2 modifiers on the nature of active sites on AuRu/ZrO2 catalysts for furfural hydrogenation
Anomalous magneto-oscillations in two-dimensional systems
The frequencies of Shubnikov-de Haas oscillations have long been used to
measure the unequal population of spin-split two-dimensional subbands in
inversion asymmetric systems. We report self-consistent numerical calculations
and experimental results which indicate that these oscillations are not simply
related to the zero-magnetic-field spin-subband densities.Comment: 4 pages, 3 figures; changed content (clarifications
Spectral Properties of Three Dimensional Layered Quantum Hall Systems
We investigate the spectral statistics of a network model for a three
dimensional layered quantum Hall system numerically. The scaling of the
quantity is used to determine the critical exponent for
several interlayer coupling strengths. Furthermore, we determine the level
spacing distribution as well as the spectral compressibility at
criticality. We show that the tail of decays as with
and also numerically verify the equation
, where is the correlation dimension and the
spatial dimension.Comment: 4 pages, 5 figures submitted to J. Phys. Soc. Jp
Test for entanglement using physically observable witness operators and positive maps
Motivated by the Peres-Horodecki criterion and the realignment criterion we
develop a more powerful method to identify entangled states for any bipartite
system through a universal construction of the witness operator. The method
also gives a new family of positive but non-completely positive maps of
arbitrary high dimensions which provide a much better test than the witness
operators themselves. Moreover, we find there are two types of positive maps
that can detect 2xN and 4xN bound entangled states. Since entanglement
witnesses are physical observables and may be measured locally our construction
could be of great significance for future experiments.Comment: 6 pages, 1 figure, revtex4 styl
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