Johannes Kepler University of Linz

About: Johannes Kepler University of Linz is a education organization based out in Linz, Oberösterreich, Austria. It is known for research contribution in the topics: Computer science & Thin film. The organization has 6605 authors who have published 19243 publications receiving 385667 citations.

Enhanced beat tracking with context-aware neural networks

Abstract: We present two new beat tracking algorithms based on the autocorrelation analysis, which showed state-of-the-art performance in the MIREX 2010 beat tracking contest. Unlike the traditional approach of processing a list of onsets, we propose to use a bidirectional Long Short-Term Memory recurrent neural network to perform a frame by frame beat classification of the signal. As inputs to the network the spectral features of the audio signal and their relative differences are used. The network transforms the signal directly into a beat activation function. An autocorrelation function is then used to determine the predominant tempo to eliminate the erroneously detected - or complement the missing - beats. The first algorithm is tuned for music with constant tempo, whereas the second algorithm is further capable to follow changes in tempo and time signature.

Key role of the wetting layer in revealing the hidden path of Ge/Si(001) Stranski-Krastanow growth onset

Abstract: The commonly accepted Stranski-Krastanow model, according to which island formation occurs on top of a wetting layer (WL) of a certain thickness, predicts for the morphological evolution an increasing island aspect ratio with volume. We report on an apparent violation of this thermodynamic understanding of island growth with deposition. In order to investigate the actual onset of three-dimensional islanding and the critical WL thickness in the Ge/Si(001) system, a key issue is controlling the Ge deposition with extremely high resolution [0.025 monolayer (ML)]. Atomic force microscopy and photoluminescence measurements on samples covering the deposition range 1.75--6.1 ML, taken along a Ge deposition gradient on 4 in. Si substrates and at different growth temperatures $({T}_{\text{g}})$, surprisingly reveal that for ${T}_{\text{g}}g675\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ steeper multifaceted domes apparently nucleate prior to shallow {105}-faceted pyramids, in a narrow commonly overlooked deposition range. The puzzling experimental findings are explained by a quantitative modeling of the total energy with deposition. We accurately matched ab initio calculations of layer and surface energies to finite-element method simulations of the elastic energy in islands, in order to compare the thermodynamic stability of different island shapes with respect to an increasing WL thickness. Close agreement between modeling and experiments is found, pointing out that the sizeable progressive lowering of the surface energy in the first few MLs of the WL reverts the common understanding of the SK growth onset. Strong similarities between islanding in SiGe and III/V systems are highlighted.

3D Imaging of Individual Ion Channels in Live Cells at 40nm Resolution

Abstract: High affinity binding of fluorescence labeled hongotoxin (HgTX1-Cy5) to the potassium channel KV1.3 in T-lymphocyte cell membranes was utilized for imaging single ion channels optically, employing Single Dye Tracing (SDT). Binding sites were seen as single fluorescence peaks in cross-sections through the cell. Their number matched, at conditions of saturated binding, the number of sites expected from biochemical determination. By fitting the peaks to the point-spread-function, well approximated by a Gaussian distribution, resolution of channel positions to within ±40nm was obtained in all three dimensions. Within the focal plane (x-y plane) positional resolution is given by the accuracy of determining the peak position of the Gaussian. The positional resolution along the optical axis (z-direction) was obtained from the accuracy of estimating the position of minimum defocusing for a single molecule. For this, the width of the fluorescence peaks in consecutive images, taken at different degrees of defocusing, were shown to accurately match the theoretical prediction, yielding ∼40nm accuracy of finding the z-position of the labeled channels. This first visualization of individual membrane proteins in live cells by fluorescence labeled ligands with 40nm 3D positional resolution opens new perspectives for the study of cellular organization and processes at the molecular level.