3,652 research outputs found
Anharmonicity due to Electron-Phonon Coupling in Magnetite
We present the results of inelastic x-ray scattering for magnetite and
analyze the energies and spectral widths of the phonon modes with different
symmetries in a broad range of temperature 125<T<293 K. The phonon modes with
X_4 and Delta_5 symmetries broaden in a nonlinear way with decreasing
temperature when the Verwey transition is approached. It is found that the
maxima of phonon widths occur away from high-symmetry points which indicates
the incommensurate character of critical fluctuations. Strong phonon
anharmonicity induced by electron-phonon coupling is discovered within ab
initio calculations which take into account local Coulomb interactions at Fe
ions. It (i) explains observed anomalous phonon broadening, and (ii)
demonstrates that the Verwey transition is a cooperative phenomenon which
involves a wide spectrum of phonons coupled to charge fluctuations condensing
in the low-symmetry phase.Comment: 5 pages, 5 figures, accepted in Physical Review Letter
Ag on Ge(111): 2D X-ray structure analysis of the (Wurzel)3 x (Wurzel)3 superstructure
We have studied the Ag/Ge(111)(Wurzel)3 x (Wurzel)3 superstructure by grazing-incidence X-ray diffraction. In our structural analysis we find striking similarities to the geometry of Au on Si(111). The Ag atoms form trimer clusters with an Ag-Ag distance of 2.94+-0.04°A with the centers of the trimers being located at the origins of the (Wurzel)3 x (Wurzel)3 lattice. The Ag layer is incomplete and at least one substrate layer is distorted
Short-Range Correlations in Magnetite above the Verwey Temperature
Magnetite, FeO, is the first magnetic material discovered and
utilized by mankind in Ancient Greece, yet it still attracts attention due to
its puzzling properties. This is largely due to the quest for a full and
coherent understanding of the Verwey transition that occurs at K and
is associated with a drop of electric conductivity and a complex structural
phase transition. A recent detailed analysis of the structure, based on single
crystal diffraction, suggests that the electron localization pattern contains
linear three-Fe-site units, the so-called trimerons. Here we show that whatever
the electron localization pattern is, it partially survives up to room
temperature as short-range correlations in the high-temperature cubic phase,
easily discernible by diffuse scattering. Additionally, {\it ab initio}
electronic structure calculations reveal that characteristic features in these
diffuse scattering patterns can be correlated with the Fermi surface topology.Comment: 7 pages, 6 figure
Russet Susceptibility in Apple Is Associated with Skin Cells that Are Larger, More Variable in Size, and of Reduced Fracture Strain
Russeting is an economically important surface disorder in apple (Malus × domestica Borkh). Indirect evidence suggests an irregular skin structure may be the cause of the phenomenon. The objective of this study was to characterize epidermal and hypodermal cell morphology and the mechanical properties of the skins of apple cultivars of differing russet susceptibility. Dimensions of epidermal and hypodermal cells were determined using microscopy. Stiffness (S), maximum force (Fmax), and maximum strain (εmax) at failure were quantified using uniaxial tensile tests of skin strips. Particularly during early fruit development, epidermal cells (EC) and hypodermal cells (HC) in russet non-susceptible cultivars occurred in greater numbers per unit area than in russet-susceptible ones. The EC and HC were lower in height, shorter in length, and of reduced tangential surface area. There were little differences in S or Fmax between non-susceptible and susceptible cultivars. However, the εmax were higher for the skins of non-susceptible cultivars, than for those of susceptible ones. This difference was larger for the young than for the later growth stages. It is concluded that russet-susceptible cultivars generally have larger cells and a wider distribution of cell sizes for both EC and HC. These result in decreased εmax for the skin during early fruit development when russet susceptibility is high. This increases the chances of skin failures which is known to trigger russeting
An Investigation of Monotonic Transducers for Large-Scale Automatic Speech Recognition
The two most popular loss functions for streaming end-to-end automatic speech
recognition (ASR) are the RNN-Transducer (RNN-T) and the connectionist temporal
classification (CTC) objectives. Both perform an alignment-free training by
marginalizing over all possible alignments, but use different transition rules.
Between these two loss types we can classify the monotonic RNN-T (MonoRNN-T)
and the recently proposed CTC-like Transducer (CTC-T), which both can be
realized using the graph temporal classification-transducer (GTC-T) loss
function. Monotonic transducers have a few advantages. First, RNN-T can suffer
from runaway hallucination, where a model keeps emitting non-blank symbols
without advancing in time, often in an infinite loop. Secondly, monotonic
transducers consume exactly one model score per time step and are therefore
more compatible and unifiable with traditional FST-based hybrid ASR decoders.
However, the MonoRNN-T so far has been found to have worse accuracy than RNN-T.
It does not have to be that way, though: By regularizing the training - via
joint LAS training or parameter initialization from RNN-T - both MonoRNN-T and
CTC-T perform as well - or better - than RNN-T. This is demonstrated for
LibriSpeech and for a large-scale in-house data set.Comment: Submitted to Interspeech 202
Brain transcriptomes of honey bees (Apis mellifera) experimentally infected by two pathogens: Black queen cell virus and Nosema ceranae.
This is the final version of the article. Available from Elsevier via the DOI in this record.Regulation of gene expression in the brain plays an important role in behavioral plasticity and decision making in response to external stimuli. However, both can be severely affected by environmental factors, such as parasites and pathogens. In honey bees, the emergence and re-emergence of pathogens and potential for pathogen co-infection and interaction have been suggested as major components that significantly impaired social behavior and survival. To understand how the honey bee is affected and responds to interacting pathogens, we co-infected workers with two prevalent pathogens of different nature, the positive single strand RNA virus Black queen cell virus (BQCV), and the Microsporidia Nosema ceranae, and explored gene expression changes in brains upon single infections and co-infections. Our data provide an important resource for research on honey bee diseases, and more generally on insect host-pathogen and pathogen-pathogen interactions. Raw and processed data are publicly available in the NCBI/GEO database: (http://www.ncbi.nlm.nih.gov/geo/) under accession number GSE81664.Sequencing was performed thanks to the EU-funded 7th Framework project BEE DOC, Grant Agreement 244956. The authors thank Maureen Labarussias for technical support during bee experiments and preparation for sequencing
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