Local Reorientation Dynamics of Semiflexible Polymers in the Melt

The reorientation dynamics of local tangent vectors of chains in isotropic amorphous melts containing semiflexible model polymers was studied by molecular dynamics simulations. The reorientation is strongly influenced both by the local chain stiffness and by the overall chain length. It takes place by two different subsequent processes: A short-time non-exponential decay and a long-time exponential reorientation arising from the relaxation of medium-size chain segments. Both processes depend on stiffness and chain length. The strong influence of the chain length on the chain dynamics is in marked contrast to its negligible effect on the static structure of the melt. The local structure shows only a small dependence on the stiffness, and is independent of chain length. Calculated correlation functions related to double-quantum NMR experiments are in qualitative agreement with experiments on entangled melts. A plateau is observed in the dependence of segment reorientation on the mean-squared displacement of the corresponding chain segments. This plateau confirms, on one hand, the existence of reptation dynamics. On the other hand, it shows how the reptation picture has to be adapted if, instead of fully flexible chains, semirigid chains are considered.Comment: 29 pages, several figures, accepted by Macromolecule

Alfv\'en-dynamo balance and magnetic excess in MHD turbulence

3D Magnetohydrodynamic (MHD) turbulent flows with initially magnetic and kinetic energies at equipartition spontaneously develop a magnetic excess (or residual energy), as well in numerical simulations and in the solar wind. Closure equations obtained in 1983 describe the residual spectrum as being produced by a dynamo source proportional to the total energy spectrum, balanced by a linear Alfv\'en damping term. A good agreement was found in 2005 with incompressible simulations; however, recent solar wind measurements disagree with these results. The previous dynamo-Alfv\'en theory is generalized to a family of models, leading to simple relations between residual and total energy spectra. We want to assess these models in detail against MHD simulations and solar wind data. The family of models is tested against compressible decaying MHD simulations with low Mach number, low cross-helicity, zero mean magnetic field, without or with expansion terms (EBM or expanding box model). A single dynamo-Alfv\'en model is found to describe correctly both solar wind scalings and compressible simulations without or with expansion. It is equivalent to the 1983-2005 closure equation but with critical balance of nonlinear turnover and linear Alfv\'en times, while the dynamo source term remains unchanged. The discrepancy with previous incompressible simulations is elucidated. The model predicts a linear relation between the spectral slopes of total and residual energies $m_R = -1/2 + 3/2 m_T$. Examining the solar wind data as in \cite{2013ApJ...770..125C}, our relation is found to be valid whatever the cross-helicity, even better so at high cross-helicity, with the total energy slope varying from $1.7$ to $1.55$.Comment: 7 pages, 7 figures, accepted for publication in A&

Online Resumes: Optimizing Design to Service Recruiters

Despite the increasing number of publications in e-Recruiting, there is still scant research on the specific requirements of online resume fields, in particular from the recruiters’ perspective. In this paper, the fields for resume forms are investigated by analyzing literature, interviewing recruiters and systematically categorizing and content-analyzing the resume fields of the 40 largest Dutch e- Recruiting sites. The findings reflect the main categories currently used in online resume forms: current career status, desired job, education, work experience, extracurricular activities, skills and personal and contact information. These identified online resume fields are discussed in light of prior resume design literature and compared with resume requirements derived from interviewing recruiters. Recommendations for resume design theory and practice are proposed

Local chain ordering in amorphous polymer melts: Influence of chain stiffness

Molecular dynamics simulation of a generic polymer model is applied to study melts of polymers with different types of intrinsic stiffness. Important static observables of the single chain such as gyration radius or persistence length are determined. Additionally we investigate the overall static melt structure including pair correlation function, structure function and orientational correlation function.Comment: 13 pages, 15 figures, PCCP accepte

First results with the boloSource() algorithm: Photometry of faint standard stars observed by Herschel/PACS

The boloSource() algorithm is a tool to separate the signal of compact sources from that of the diffuse background in the timeline of far-infrared measurements performed by the PACS camera of the Herschel Space Observatory. An important characteristic and quality indicator of this method is that how well it can reproduce the flux of faint standard stars which have reliable flux estimates. For this propose we selected a few calibrator targets and constructed light curves by extracting point source flux for each repetition of the measurements independently using standard aperture photometry methods. These were compared with the light curves obtained using the boloSource() method on the same dataset. The results indicate that boloSource() provides a similar level of photometric accuracy and reproducibility as the usual flux extraction and photometry methods. This new technique will be developed further and also tested against other methods in more complex fields with the goal to make it usable for large-scale studies in the future.Comment: 10 pages, 7 figures, 4 table

Vom Ende des jüdischen Schulwesens in Breslau

Der nachfolgende Bericht basiert auf dem Manuskript für einen Vortrag vor Mitgliedern des Verbandes ehemaliger Breslauer in Israel im September 2006. Viele der heute dort lebenden ehemaligen Breslauer waren Schülerinnen und Schüler der jüdischen Schulen in ihrer Heimatstadt. Das Ende des jüdischen Schulwesens wird im Folgenden vor allem nach den im (polnischen) Staatsarchiv zu Breslau [Archivum Panstwowe we Wrocławia] befindlichen Akten des Magistrats der schlesischen (Provinz) Hauptstadt Breslau und darunter insbesondere den der Magistratsschulverwaltung und soweit Dokumente darüber vorlagen für die Zeit zwischen 1933 und 1942 in groben Zügen aufgezeichnet. Auf die Wiederholung von Einzelheiten, die bereits in anderen Publikationen veröffentlicht wurden, und die breite Einbeziehung anderer Quellen wurde im Sinne, einen Überblick über die Ereignisse und die betroffenen Schüler und Lehrer zu vermitteln, verzichtet. Eine umfangreichere Arbeit mit vielen weiteren Details, die sich aus den Archivalien in Wrocław / Breslau ergeben und die auch anderes Quellenmaterial mit einschließt, ist unter dem Arbeitstitel „Breslaus jüdische Schüler, Lehrer und Schulen 1919 – 1943“ in Vorbereitung. Diese geplante Publikation und der vorliegende Artikel sollen dazu beitragen, dass das Andenken an die Opfer des nationalsozialistischen Regimes gewahrt wird. Deshalb werden auch die Namen der Lehrer, von denen viele ermordet wurden, genannt. Sie sollen unvergessen bleiben. Zugleich sollen über diese Veröffentlichung Kontakte zu anderen Forschern, die sich auch mit der Thematik der Jüdischen Schulen in der Zeit der Weimarer Republik und während der Herrschaft des Nationalsozialismus befassen, hergestellt und weitere Berichte von Zeitzeugen und Dokumente erschlossen werden, um dazu beizutragen, Einzelschicksale bzw. Lebenswege von Lehrern und Schülern und auch von jenen, die sich schuldig gemacht haben, aufzudecken

Three-dimensional Iroshnikov-Kraichnan turbulence in a mean magnetic field

Forced, weak MHD turbulence with guide field is shown to adopt different regimes, depending on the magnetic excess of the large forced scales. When the magnetic excess is large enough, the classical perpendicular cascade with $5/3$ scaling is obtained, while when equipartition is imposed, an isotropic $3/2$ scaling appears in all directions with respect to the mean field (\cite{2010PhRvE..82b6406G} or GM10). We show here that the $3/2$ scaling of the GM10 regime is not ruled by a small-scale cross-helicity cascade, and propose that it is a 3D extension of a perpendicular weak Iroshnikov-Kraichnan (IK) cascade. We analyze in detail the structure functions in real space and show that they closely follow the critical balance relation both in the local frame and the global frame: we show that there is no contradiction between this and the isotropic $3/2$ scaling of the spectra. We propose a scenario explaining the spectral structure of the GM10 regime, that starts with a perpendicular weak IK cascade and extends to 3D by using quasi-resonant couplings. The quasi-resonance condition happens to reduce the energy flux in the same way as is done in the weak perpendicular cascade, so leading to a $3/2$ scaling in all directions. We discuss the possible applications of these findings to solar wind turbulence.Comment: Major re-write of manuscrip