494 research outputs found
Bands, resonances, edge singularities and excitons in core level spectroscopy investigated within the dynamical mean field theory
Using a recently developed impurity solver we exemplify how dynamical mean
field theory captures band excitations, resonances, edge singularities and
excitons in core level x-ray absorption (XAS) and core level photo electron
spectroscopy (cPES) on metals, correlated metals and Mott insulators. Comparing
XAS at different values of the core-valence interaction shows how the
quasiparticle peak in the absence of core-valence interactions evolves into a
resonance of similar shape, but different origin. Whereas XAS is rather
insensitive to the metal insulator transition, cPES can be used, due to
nonlocal screening, to measure the amount of local charge fluctuation
Teaching deep neural networks to localize sources in super-resolution microscopy by combining simulation-based learning and unsupervised learning
Single-molecule localization microscopy constructs super-resolution images by the sequential imaging and computational localization of sparsely activated fluorophores. Accurate and efficient fluorophore localization algorithms are key to the success of this computational microscopy method. We present a novel localization algorithm based on deep learning which significantly improves upon the state of the art. Our contributions are a novel network architecture for simultaneous detection and localization, and a new training algorithm which enables this deep network to solve the Bayesian inverse problem of detecting and localizing single molecules. Our network architecture uses temporal context from multiple sequentially imaged frames to detect and localize molecules. Our training algorithm combines simulation-based supervised learning with autoencoder-based unsupervised learning to make it more robust against mismatch in the generative model. We demonstrate the performance of our method on datasets imaged using a variety of point spread functions and fluorophore densities. While existing localization algorithms can achieve optimal localization accuracy in data with low fluorophore density, they are confounded by high densities. Our method significantly outperforms the state of the art at high densities and thus, enables faster imaging than previous approaches. Our work also more generally shows how to train deep networks to solve challenging Bayesian inverse problems in biology and physics
High-density correlation energy expansion of the one-dimensional uniform electron gas
We show that the expression of the high-density (i.e small-) correlation
energy per electron for the one-dimensional uniform electron gas can be
obtained by conventional perturbation theory and is of the form \Ec(r_s) =
-\pi^2/360 + 0.00845 r_s + ..., where is the average radius of an
electron. Combining these new results with the low-density correlation energy
expansion, we propose a local-density approximation correlation functional,
which deviates by a maximum of 0.1 millihartree compared to the benchmark DMC
calculations.Comment: 7 pages, 2 figures, 3 tables, accepted for publication in J. Chem.
Phy
Fast amortized inference of neural activity from calcium imaging data with variational autoencoders
Solar radiative transfer simulations in Saharan dust plumes: particle shapes and 3-D effect
Radiative fields of three-dimensional inhomogeneous Saharan dust clouds have been calculated at solar wavelength (0.6 μm) by means of a Monte Carlo radiative transfer model. Scattering properties are taken from measurements in the SAMUM campaigns, from light scattering calculations for spheroids based on the MIESCHKA code, from Mie theory for spheres and from the geometric optics method assuming irregular shaped particles. Optical properties of different projected area equivalent shapes are compared. Large differences in optical properties are found especially in the phase functions.
Results of radiative transfer calculations based on the Monte Carlo method are shown exemplarily for one dust cloud simulated by the cloud resolving atmospheric circulation model LM-MUSCAT-DES. Shape-induced differences in the radiation fluxes are pronounced, for example, the domain averaged normalized radiance is about 30% lower in the case of a dust plume consisting of spheroids or irregular particles compared to spheres. The effect of net horizontal photon transport (3-D effect) on the reflected radiance fields is only notable at the largest gradients in optical thickness. For example, the reflectance at low sun position differs locally about 15% when horizontal photon transport is accounted for. ‘Sharp edges' due to 1-D calculations are smoothed out in the 3-D case
Electronic depth profiles with atomic layer resolution from resonant soft x-ray reflectivity
The analysis of x-ray reflectivity data from artificial heterostructures
usually relies on the homogeneity of optical properties of the constituent
materials. However, when the x-ray energy is tuned to an absorption edge, this
homogeneity no longer exists. Within the same material, spatial regions
containing elements at resonance will have optical properties very different
from regions without resonating sites. In this situation, models assuming
homogeneous optical properties throughout the material can fail to describe the
reflectivity adequately. As we show here, resonant soft x-ray reflectivity is
sensitive to these variations, even though the wavelength is typically large as
compared to the atomic distances over which the optical properties vary. We
have therefore developed a scheme for analyzing resonant soft x-ray
reflectivity data, which takes the atomic structure of a material into account
by "slicing" it into atomic planes with characteristic optical properties.
Using LaSrMnO4 as an example, we discuss both the theoretical and experimental
implications of this approach. Our analysis not only allows to determine
important structural information such as interface terminations and stacking of
atomic layers, but also enables to extract depth-resolved spectroscopic
information with atomic resolution, thus enhancing the capability of the
technique to study emergent phenomena at surfaces and interfaces.Comment: Completely overhauled with respect to the previous version due to
peer revie
Overview: Tropospheric profiling: state of the art and future challenges – introduction to the AMT special issue
Abstract. This paper introduces the Atmospheric Measurement Techniques special issue on tropospheric profiling, which was conceived to host full papers presenting the results shown at the 9th International Symposium on Tropospheric Profiling (ISTP9). ISTP9 was held in L'Aquila (Italy) from 3 to 7 September 2012, bringing together 150 scientists representing of 28 countries and 3 continents. The tropospheric profiling special issue collects the highlights of ISTP9, reporting recent advances and future challenges in research and technology development
Quantitative determination of bond order and lattice distortions in nickel oxide heterostructures by resonant x-ray scattering
We present a combined study of Ni -edge resonant x-ray scattering and
density functional calculations to probe and distinguish electronically driven
ordering and lattice distortions in nickelate heterostructures. We demonstrate
that due to the low crystal symmetry, contributions from structural distortions
can contribute significantly to the energy-dependent Bragg peak intensities of
a bond-ordered NdNiO reference film. For a LaNiO-LaAlO superlattice
that exhibits magnetic order, we establish a rigorous upper bound on the
bond-order parameter. We thus conclusively confirm predictions of a dominant
spin density wave order parameter in metallic nickelates with a
quasi-two-dimensional electronic structure
Strain and composition dependence of the orbital polarization in nickelate superlattices
A combined analysis of x-ray absorption and resonant reflectivity data was
used to obtain the orbital polarization profiles of superlattices composed of
four-unit-cell-thick layers of metallic LaNiO3 and layers of insulating RXO3
(R=La, Gd, Dy and X=Al, Ga, Sc), grown on substrates that impose either
compressive or tensile strain. This superlattice geometry allowed us to partly
separate the influence of epitaxial strain from interfacial effects controlled
by the chemical composition of the insulating blocking layers. Our quantitative
analysis reveal orbital polarizations up to 25%. We further show that strain is
the most effective control parameter, whereas the influence of the chemical
composition of the blocking layers is comparatively small.Comment: 9 pages, 8 figure
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