3,834 research outputs found
Bounds on Lorentz and CPT Violation from the Earth-Ionosphere Cavity
Electromagnetic resonant cavities form the basis of many tests of Lorentz
invariance involving photons. The effects of some forms of Lorentz violation
scale with cavity size. We investigate possible signals of violations in the
naturally occurring resonances formed in the Earth-ionosphere cavity.
Comparison with observed resonances places the first terrestrial constraints on
coefficients associated with dimension-three Lorentz-violating operators at the
level of 10^{-20} GeV.Comment: 8 pages REVTe
Orbital order in La0.5Sr1.5MnO4: beyond a common local Jahn-Teller picture
The standard way to find the orbital occupation of Jahn-Teller (JT) ions is
to use structural data, with the assumption of a one-to-one correspondence
between the orbital occupation and the associated JT distortion, e.g. in O6
octahedron. We show, however, that this approach in principle does not work for
layered systems. Specifically, using the layered manganite La0.5Sr1.5MnO4 as an
example, we found from our x-ray absorption measurements and theoretical
calculations, that the type of orbital ordering strongly contradicts the
standard local distortion approach for the Mn3+O6 octahedra, and that the
generally ignored long-range crystal field effect and anisotropic hopping
integrals are actually crucial to determine the orbital occupation. Our
findings may open a pathway to control of the orbital state in multilayer
systems and thus of their physical properties.Comment: 4+ pages, 4 figure
A Complete Version of the Glauber Theory for Elementary Atom - Target Atom Scattering and Its Approximations
A general formalism of the Glauber theory for elementary atom (EA) - target
atom (TA) scattering is developed. A second-order approximation of its complete
version is considered in the framework of the optical-model perturbative
approach. A `potential' approximation of a second-order optical model is
formulated neglecting the excitation effects of the TA. Its accuracy is
evaluated within the second-order approximation for the complete version of the
Glauber EA-TA scattering theory.Comment: PDFLaTeX, 10 pages, no figures; an updated versio
SODAR Core: a Django-based framework for scientific data management and analysis web apps
Modern life science is generating large data sets at a unprecedented speed. A major source of data are so-called omics (e.g., genomics, metabolomics, or proteomics) experiments. Consequently, management and analysis of scientific data has become a major challenge. Further, the heterogeneity of projects makes "one size fits all" data analysis systems infeasible and calls for specialized data analysis platforms.
The authors are actively developing applications for the FAIR (findable, accessible, interoperable, and reuseable) data management of omics data and their analysis. In order to prevent duplication of work, we have extracted the commonly useful components into SODAR Core, a Python framework on top of Django. It is used in our actively developed applications and also proved useful in internal web app prototypes.
Examples for using SODAR Core in the development of scientific data management web apps is Digestiflow and the Filesfolders module shipping with SODAR Core. An example for using SODAR Core in the development of scientific data analysis web apps is VarFis
The CoESCA station at BESSY: Auger electron–photoelectron coincidences from surfaces demonstrated for Ag MNN
In this work, we present the CoESCA station for electron–electron coincidence spectroscopy from surfaces, built in a close collaboration between Uppsala University and Helmholtz-Zentrum Berlin at the BESSY II synchrotron facility in Berlin, Germany. We start with a detailed overview of previous work in the field of electron–electron coincidences, before we describe the CoESCA setup and its design parameters. The system is capable of recording shot-to-shot resolved 6D coincidence datasets, i.e. the kinetic energy and the two take off angles for both coincident electrons. The mathematics behind extracting and analysing these multi-dimensional coincidence datasets is introduced, with a focus on coincidence statistics, resulting in fundamental limits of the signal-to-noise ratio and its implications for acquisition times and the size of the raw data stream. The functionality of the CoESCA station is demonstrated for the example of Auger electron–photoelectron coincidences from silver surfaces for photoelectrons from the Ag 3d core levels and their corresponding MNN Auger electrons. The Auger spectra originating from the different core levels, 3d and 3d could be separated and further, the two-hole state energy distributions were determined for these Auger decay channels
Size effect on magnetism of Fe thin films in Fe/Ir superlattices
In ferromagnetic thin films, the Curie temperature variation with the
thickness is always considered as continuous when the thickness is varied from
to atomic planes. We show that it is not the case for Fe in Fe/Ir
superlattices. For an integer number of atomic planes, a unique magnetic
transition is observed by susceptibility measurements, whereas two magnetic
transitions are observed for fractional numbers of planes. This behavior is
attributed to successive transitions of areas with and atomic planes,
for which the 's are not the same. Indeed, the magnetic correlation length
is presumably shorter than the average size of the terraces. Monte carlo
simulations are performed to support this explanation.Comment: LaTeX file with Revtex, 5 pages, 5 eps figures, to appear in Phys.
Rev. Let
Finite-size scaling in thin Fe/Ir(100) layers
The critical temperature of thin Fe layers on Ir(100) is measured through
M\"o{\ss}bauer spectroscopy as a function of the layer thickness. From a
phenomenological finite-size scaling analysis, we find an effective shift
exponent lambda = 3.15 +/- 0.15, which is twice as large as the value expected
from the conventional finite-size scaling prediction lambda=1/nu, where nu is
the correlation length critical exponent. Taking corrections to finite-size
scaling into account, we derive the effective shift exponent
lambda=(1+2\Delta_1)/nu, where Delta_1 describes the leading corrections to
scaling. For the 3D Heisenberg universality class, this leads to lambda = 3.0
+/- 0.1, in agreement with the experimental data. Earlier data by Ambrose and
Chien on the effective shift exponent in CoO films are also explained.Comment: Latex, 4 pages, with 2 figures, to appear in Phys. Rev. Lett
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