1,526 research outputs found
Rate-dependent morphology of Li2O2 growth in Li-O2 batteries
Compact solid discharge products enable energy storage devices with high
gravimetric and volumetric energy densities, but solid deposits on active
surfaces can disturb charge transport and induce mechanical stress. In this
Letter we develop a nanoscale continuum model for the growth of Li2O2 crystals
in lithium-oxygen batteries with organic electrolytes, based on a theory of
electrochemical non-equilibrium thermodynamics originally applied to Li-ion
batteries. As in the case of lithium insertion in phase-separating LiFePO4
nanoparticles, the theory predicts a transition from complex to uniform
morphologies of Li2O2 with increasing current. Discrete particle growth at low
discharge rates becomes suppressed at high rates, resulting in a film of
electronically insulating Li2O2 that limits cell performance. We predict that
the transition between these surface growth modes occurs at current densities
close to the exchange current density of the cathode reaction, consistent with
experimental observations.Comment: 8 pages, 6 fig
Rieger, Schwabe, Suess-de Vries: The Sunny Beats of Resonance
We propose a self-consistent explanation of Rieger-type periodicities, the
Schwabe cycle, and the Suess-de Vries cycle in terms of resonances of various
wave phenomena with gravitational forces exerted by the orbiting planets.
Starting on the high-frequency side, we show that the two-planet spring tides
of Venus, Earth and Jupiter are able to excite magneto-Rossby waves which can
be linked with typical Rieger-type periods. We argue then that the 11.07-year
beat period of those magneto-Rossby waves synchronizes an underlying
conventional -dynamo, by periodically changing either the field
storage capacity in the tachocline or some portion of the -effect
therein. We also strengthen the argument that the Suess-de Vries cycle appears
as an 193-year beat period between the 22.14-year Hale cycle and a spin-orbit
coupling effect related with the 19.86-year rosette-like motion of the Sun
around the barycenter.Comment: 31 pages, 12 figure
Surface resonance of the (2Ă1) reconstructed lanthanum hexaboride (001)-cleavage plane : a combined STM and DFT study
We performed a combined study of the (001)-cleavage plane of lanthanum hexaboride (LaB6) using scanning tunneling microscopy and density-functional theory (DFT). Experimentally, we found a (2Ă1) reconstructed surface on a local scale. The reconstruction is only short-range ordered and tends to order perpendicularly to step edges. At larger distances from surface steps, the reconstruction evolves to a labyrinthlike pattern. These findings are supported by low-energy electron diffraction experiments. Slab calculations within the framework of DFT show that the atomic structure consists of parallel lanthanum chains on top of boron octahedra. Scanning tunneling spectroscopy shows a prominent spectral feature at â0.6eV. Using DFT, we identify this structure as a surface resonance of the (2Ă1) reconstructed LaB6 (100) surface which is dominated by boron dangling bond states and lanthanum d states
On the robustness of entanglement in analogue gravity systems
We investigate the possibility of generating quantum-correlated quasi-particles utilizing analogue gravity systems. The quantumness of these correlations is a key aspect of analogue gravity effects and their presence allows for a clear separation between classical and quantum analogue gravity effects. However, experiments in analogue systems, such as BoseâEinstein condensates (BECs) and shallow water waves, are always conducted at non-ideal conditions, in particular, one is dealing with dispersive media at non-zero temperatures. We analyse the influence of the initial temperature on the entanglement generation in analogue gravity phenomena. We lay out all the necessary steps to calculate the entanglement generated between quasi-particle modes and we analytically derive an upper bound on the maximal temperature at which given modes can still be entangled. We further investigate a mechanism to enhance the quantum correlations. As a particular example, we analyse the robustness of the entanglement creation against thermal noise in a sudden quench of an ideally homogeneous BEC, taking into account the super-sonic dispersion relations
Wavelet Analysis for Wind Fields Estimation
Wind field analysis from synthetic aperture radar images allows the estimation of wind direction and speed based on image descriptors. In this paper, we propose a framework to automate wind direction retrieval based on wavelet decomposition associated with spectral processing. We extend existing undecimated wavelet transform approaches, by including Ă trous with B3 spline scaling function, in addition to other wavelet bases as Gabor and Mexican-hat. The purpose is to extract more reliable directional information, when wind speed values range from 5 to 10 msâ1. Using C-band empirical models, associated with the estimated directional information, we calculate local wind speed values and compare our results with QuikSCAT scatterometer data. The proposed approach has potential application in the evaluation of oil spills and wind farms
Surface resonance of the (21) reconstructed lanthanum hexaboride (001)-cleavage plane: a combined STM and DFT study
We performed a combined study of the (001)-cleavage plane of lanthanum
hexaboride (LaB) using scanning tunneling microscopy (STM) and
density functional theory (DFT). Experimentally, we found a (21)
reconstructed surface on a local scale. The reconstruction is only short-range
ordered and tends to order perpendicularly to step edges. At larger distances
from surface steps, the reconstruction evolves to a labyrinth-like pattern.
These findings are supported by low-energy electron diffraction (LEED)
experiments. Slab calculations within the framework of DFT shows that the
atomic structure consists of parallel lanthanum chains on top of boron
octahedra. Scanning tunneling spectroscopy (STS) shows a prominent spectral
feature at -0.6 eV. Using DFT, we identify this structure as a surface
resonance of the (21) reconstructed LaB (100)-surface which
is dominated by boron dangling bond-states and lanthanum d-states.Comment: 10 pages, 16 figure
On an exponential attractor for a class of PDEs with degenerate diffusion and chemotaxis
In this article we deal with a class of strongly coupled parabolic systems
that encompasses two different effects: degenerate diffusion and chemotaxis.
Such classes of equations arise in the mesoscale level modeling of biomass
spreading mechanisms via chemotaxis. We show the existence of an exponential
attractor and, hence, of a finite-dimensional global attractor under certain
'balance conditions' on the order of the degeneracy and the growth of the
chemotactic function
Coatings for FEL optics preparation and characterization of B4C and Pt
Large X ray mirrors are required for beam transport at both present day and future free electron lasers FELs and synchrotron sources worldwide. The demand for large mirrors with lengths up to 1 m single layers consisting of light or heavy elements has increased during the last few decades. Accordingly, surface finishing technology is now able to produce large substrate lengths with micro roughness on the sub nanometer scale. At the Helmholtz Zentrum Geesthacht HZG , a 4.5 m long sputtering facility enables us to deposit a desired single layer material some tens of nanometers thick. For the European XFEL project, the shape error should be less than 2 nm over the whole 1 m X ray mirror length to ensure the safe and efficient delivery of X ray beams to the scientific instruments. The challenge is to achieve thin film deposition on silicon substrates, benders and gratings without any change in mirror shape. Thin films of boron carbide and platinum with a thickness in the range 30 100 nm were manufactured using the HZG sputtering facility. This setup is able to cover areas of up to 1500 mm x120 mm in one step using rectangular sputtering sources. The coatings produced were characterized using various thin film methods. It was possible to improve the coating process to achieve a very high uniformity of the layer thickness. The movement of the substrate in front of the sputtering source has been optimized. Avariation in B4C layer thickness below 1 nm peak to valley was achieved at a mean thickness of 51.8 nm over a deposition length of 1.5 m. In the case of Pt, reflectometry and micro roughness measurements were performed. The uniformity in layer thickness was about 1 nm peak to valley . The micro roughness of the Pt layers showed no significant change in the coated state for layer thicknesses of 32 nm and 102 nm compared with the uncoated substrate state. The experimental results achieved will be discussed with regard to current restrictions and future development
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