Zur Stabilität des elastischen Rotorblattes

Es wird die Stabilität der selbsterregten Schlagschwingungen eines elastischen Hubschrauber-Rotorblattes im Vorwärtsflug behandelt. Die Bewegungsgleichung wird für das Ersatzsystem einer Schwingerkette aus starren, durch Federgelenke verbundenen Teilstücken aufgestellt. Eine Aussage über die Stabilität ist durch eine numerische Rechnung in Matrizenform möglich, die eine Verfeinerung der aerodynamischen und mechanischen Annahmen zuläßt. Für ein einfaches Beispiel werden Rechengang und Ergebnis mitgeteilt.This paper deals with the transient stability of the flapping motion of a flexible helicopter rotor blade in forward flight. The equation of flapping motion is developed for the substituted system of rigid parts connected by elastic flapping hinges. It is possible to investigate the stability by computations based upon matrix equations which permit the refinement of aerodynamic and mechanic assumptions. The solution and results are given for a simple example

Ligand crowding at a nascent signal sequence

We have systematically analyzed the molecular environment of the signal sequence of a growing secretory protein from Escherichia coli using a stage- and site-specific cross-linking approach. Immediately after emerging from the ribosome, the signal sequence of pOmpA is accessible to Ffh, the protein component of the bacterial signal recognition particle, and to SecA, but it remains attached to the surface of the ribosome via protein L23. These contacts are lost upon further growth of the nascent chain, which brings the signal sequence into sole proximity to the chaperone Trigger factor (TF). In its absence, nascent pOmpA shows extended contacts with L23, and even long chains interact in these conditions proficiently with Ffh. Our results suggest that upon emergence from the ribosome, the signal sequence of an E. coli secretory protein gradually becomes sequestered by TF. Although TF thereby might control the accessibility of pOmpA's signal sequence to Ffh and SecA, it does not influence interaction of pOmpA with SecB

Duplicate Table Detection with Xash

Data lakes are typically lightly curated and as such prone to data quality problems and inconsistencies. In particular, duplicate tables are common in most repositories. The goal of duplicate table detection is to identify those tables that display the same data. Comparing tables is generally quite expensive as the order of rows and columns might differ for otherwise identical tables. In this paper, we explore the application of Xash, a hash function previously proposed for the discovery of multi-column join candidates, for the use case of duplicate table detection. With Xash, it is possible to generate a so-called super key, which serves like a bloom filter and instantly identifies the existence of particular cell values. We show that using Xash it is possible to speed up the duplicate table detection process significantly. In comparison to SimHash and other competing hash functions, Xash results in fewer false positive candidates

Electroinduced two-nucleon knockout and correlations in nuclei

We present a model to calculate cross sections for electroinduced two-nucleon emission from finite nuclei. Short-range correlations in the wave functions and meson-exchange contributions to the photoabsorption process are implemented. Effects of the short-range correlations are studied with the aid of a perturbation expansion method with various choices of the Jastrow correlation function. The model is used to investigate the relative importance of the different reaction mechanisms contributing to the A(e,e$'$pn) and A(e,e$'$pp) process. Representative examples for the target nuclei $^{12}$C and $^{16}$O and for kinematical conditions accessible with contemporary high-duty cycle electron accelerators are presented. A procedure is outlined to calculate the two-nucleon knockout contribution to the semi-exclusive (e,e$'$p) cross section. Using this technique we investigate in how far semi-exclusive (e,e$'$p) reactions can be used to detect high-momentum components in the nuclear spectral function.Comment: 51 pages, Latex, uses epsf.sty and elsart.sty, 17 figures (in eps format

A Phenomenological Description of (\pi^{-}\Delta^{++}) Photo- and Electroproduction in Nucleon Resonance Region

The (\pi^{-}\Delta^{++}) production on the nucleon by real and virtual photons is discussed as initial step in a simple model approach for the two pion photo- and electroproduction on the nucleon, with emphasis on nucleon resonance excitation which is of interest for new facilities like TJNAF. A calculation for (\pi^{-}\Delta^{++}) channel in resonance excitation region is presented and compared to existing experimental data along with a discussion of physical effects that we find to be of relevance. The calculation is proposed as a starting basis for the investigation of (N^{*}) electromagnetic form factors using experimental data about two pion production by real and virtual photons.Comment: 36 pages, 14 figures, to be published in Nucl. Phys.

The effect of fluorination on the surface structure of truxenones

LAR, AJR and TSJ acknowledge support from the Engineering and Physical Sciences Research Council [Grant Number EP/H021388/1]. SH and CBN acknowledge support from the following funding bodies: EPSRC Project EP/G037515/1, EC FP7 Project SC2 (610115), EC FP7 Project ArtESun (604397), and EC FP7 POLYMED (612538). The raw data associated with this article can be accessed at the following DOI: 10.17632/mmp65j8jgs.