Lattice Electrons on a Cylinder Surface in the Presence of Rational Magnetic Flux and Disorder

We consider a disordered two-dimensional system of independent lattice electrons in a perpendicular magnetic field with rigid confinement in one direction and generalized periodic boundary conditions (GPBC) in the other direction. The objects investigated numerically are the orbits in the plane spanned by the energy eigenvalues and the corresponding center of mass coordinate in the confined direction, parameterized by the phase characterizing the GPBC. The Kubo Hall conductivity is expressed in terms of the winding numbers of these orbits. For vanishing disorder the spectrum of the system consists of Harper bands with energy levels corresponding to the edge states within the band gaps. Disorder leads to broadening of the bands. For sufficiently large systems localized states occur in the band tails. We find that within the mobility gaps of bulk states the Diophantine equation determines the value of the Hall conductivity as known for systems with torus geometry (PBCs in both directions). Within the spectral bands of extended states the Hall conductivity fluctuates strongly. For sufficiently large systems the generic behavior of localization-delocalization transitions characteristic for the quantum Hall effect are recovered.Comment: RevTeX, 10 pages, 14 PostScript figure

Effects of Training on Employee Suggestions and Promotions in an Internal Labor Market

We evaluate the effects of employer-provided formal training on employee suggestions for productivity improvements and on promotions among male blue-collar workers. More than twenty years of personnel data of four entry cohorts in a German company allow us to address issues such as unobserved heterogeneity and the length of potential training effects. Our main finding is that workers have larger probabilities to make suggestions and to be promoted after they have received formal training. The effect on suggestions is however only short term. Promotion probabilities are largest directly after training but also seem to be affected in the long term.productivity, insider econometrics, human capital, promotions, training

Betriebsinterne Arbeitsmärkte, Hierarchien und Neueinstellungen: Eine empirische Untersuchung mit Personaldaten

Zusammenfassung: In dieser Arbeit werden Personalstammdaten eines großen Unternehmens des verarbeitenden Gewerbes genutzt, in der die Belegschaft in Arbeiter, technische und kaufmännische Angestellte untergliedert ist. Im Sinne von Doeringer und Piore (1971) kann gezeigt werden, dass der interne Arbeitsmarkt für Arbeiter - insbesondere für Facharbeiter - wesentlich stärker vom externen Arbeitsmarkt isoliert ist, als dies bei Angestellten der Fall ist. Die Determinanten der Besetzung der Hierarchieebenen werden mit geordneten Probitmodellen untersucht. Die hierarchischen Positionen von Arbeitern werden stärker durch die Dauer der Betriebszugehörigkeit als Proxy für spezifisches Humankapital determiniert, während die Besetzung der Hierarchie bei Angestellten wesentlich durch formale Bildungsabschlüsse und allgemeine Erfahrung determiniert wir

Equivalent circuit and continuum modeling of the impedance of electrolyte-filled pores

Batteries, supercapacitors, and several other electrochemical devices charge by accumulating ions in the pores of electrolyte-immersed porous electrodes. The charging of such devices has long been interpreted using equivalent circuits and the partial differential equations these give rise to. Here, we discuss the validity of the transmission line (TL) circuit and equation for modeling a single electrolyte-filled pore in contact with a reservoir of resistance $R_{r}$. The textbook derivation of the pore-reservoir impedance $R_r+Z_p$ from the TL equation does not correctly account for ionic current conservation at the pore-reservoir interface. However, correcting this shortcoming leads to the same impedance. We also show that the pore impedance $Z_p$ can be derived directly from the TL circuit, bypassing the TL equation completely. The TL circuit assumes equipotential lines in an electrolyte-filled pore to be straight, which is not the case near the pore entrance and end. To determine the importance of these regions, we numerically simulated the charging of pores of different lengths $\ell_p$ and radii $\varrho_p$ through the Poisson-Nernst-Planck equations. We find that pores with aspect ratios beyond $\ell_p/\varrho_p\gtrapprox5$ have impedances in good agreement with $Z_p$.Comment: 24 pages, 18 figure

A next-generation CFD tool for large-eddy simulations on the desktop

Dive deep into the fascinating world of real-time computational fluid dynam- ics. We present details of our GPU-accelerated flow solver for the simulation of non-linear violent flows in marine and coastal engineering. The solver, the efficient lattice boltzmann environment elbe, is accelerated with recent NVIDIA graphics hardware and allows for three-dimensional simulations of complex flows in or near real-time. Details of the very ef- ficient numerical back end, the pre- and postprocessing tools and the integrated OpenGL visualizer tool will be discussed. Moreover, several applications with marine relevance demonstrate that elbe can be considered as prototype for next-generation CFD tools for simulation-based design (SBD) and interactive flow field monitoring on commodity hardware

Lost in folding space? Comparing four variants of the thermodynamic model for RNA secondary structure prediction

Janssen S, Schudoma C, Steger G, Giegerich R. Lost in folding space? Comparing four variants of the thermodynamic model for RNA secondary structure prediction. BMC Bioinformatics. 2011;12(1): 429.BACKGROUND:Many bioinformatics tools for RNA secondary structure analysis are based on a thermodynamic model of RNA folding. They predict a single, "optimal" structure by free energy minimization, they enumerate near-optimal structures, they compute base pair probabilities and dot plots, representative structures of different abstract shapes, or Boltzmann probabilities of structures and shapes. Although all programs refer to the same physical model, they implement it with considerable variation for different tasks, and little is known about the effects of heuristic assumptions and model simplifications used by the programs on the outcome of the analysis.RESULTS:We extract four different models of the thermodynamic folding space which underlie the programs RNAfold, RNAshapes, and RNAsubopt. Their differences lie within the details of the energy model and the granularity of the folding space. We implement probabilistic shape analysis for all models, and introduce the shape probability shift as a robust measure of model similarity. Using four data sets derived from experimentally solved structures, we provide a quantitative evaluation of the model differences.CONCLUSIONS:We find that search space granularity affects the computed shape probabilities less than the over- or underapproximation of free energy by a simplified energy model. Still, the approximations perform similar enough to implementations of the full model to justify their continued use in settings where computational constraints call for simpler algorithms. On the side, we observe that the rarely used level 2 shapes, which predict the complete arrangement of helices, multiloops, internal loops and bulges, include the "true" shape in a rather small number of predicted high probability shapes. This calls for an investigation of new strategies to extract high probability members from the (very large) level 2 shape space of an RNA sequence. We provide implementations of all four models, written in a declarative style that makes them easy to be modified. Based on our study, future work on thermodynamic RNA folding may make a choice of model based on our empirical data. It can take our implementations as a starting point for further program development

Social Factors of Dietary Risk Behavior in Older German Adults: Results of a Multivariable Analysis

With this analysis, we aimed to examine the associations between social factors and dietary risk behavior in older adults. Data were collected through a full-population postal survey of German adults aged 65 years or older (n = 1687, 33% response proportion, 52% female, mean age = 76 years). Using principal component analysis (PCA), a data-driven Dietary Risk Behavior Index (DRB) was computed. Dietary risk behavior was defined as consumption frequencies of vegetables/fruit, whole grains, and dairy products below national dietary recommendations. By performing a multiple linear regression, we analyzed associations between sociodemographic, socioeconomic, psychosocial, and behavioral factors and dietary risk behavior. Physical activity, female gender, socioeconomic status, social support, and age (in the male sample) were negatively associated with dietary risk behavior. Alcohol consumption and smoking were positively associated with dietary risk behavior. A group-specific analysis revealed a higher goodness-of-fit for the low socioeconomic status group, older adults aged 65–79 years, and women. A comprehensive understanding of the relationships between social factors and dietary risk behavior in older adults assists the group-specific targeting of dietary-related interventions. Demand-oriented dietary interventions should account for underlying social conditions to reduce inequity in dietary risk behavior among older adults. The results of this work may be transferable to municipalities in high-income European countries.Peer Reviewe

Modified Sagnac interferometer for contact-free length measurement of a direct absorption cell

International audienceAccurate path length measurements in absorption cells are recurrent requirements in quantitative molecular absorption spectroscopy. A new twin path laser interferometer for length measurements in a simple direct path absorption geometry is presented, along with a full uncertainty budget. The path in an absorption cell is determined by measuring the optical path length change due to the diminution of the refractive index when the cell originally filled with nitrogen gas is evacuated. The performance of the instrument based on a stabilized HeNe laser is verified by comparison with the results of direct mechanical length measurements of a roughly 45 mm long, specially designed absorption cell