Calculating rotordynamic coefficients of seals by finite-difference techniques

For modelling the turbulent flow in a seal the Navier-Stokes equations in connection with a turbulence (kappa-epsilon) model are solved by a finite-difference method. A motion of the shaft round the centered position is assumed. After calculating the corresponding flow field and the pressure distribution, the rotor-dynamic coefficients of the seal can be determined. These coefficients are compared with results obtained by using the bulk flow theory of Childs and with experimental results

A 3-dimensional finite-difference method for calculating the dynamic coefficients of seals

A method to calculate the dynamic coefficients of seals with arbitrary geometry is presented. The Navier-Stokes equations are used in conjunction with the k-e turbulence model to describe the turbulent flow. These equations are solved by a full 3-dimensional finite-difference procedure instead of the normally used perturbation analysis. The time dependence of the equations is introduced by working with a coordinate system rotating with the precession frequency of the shaft. The results of this theory are compared with coefficients calculated by a perturbation analysis and with experimental results

Molecular phylogeography and colonisation history of passerine birds of the Atlantic islands (Macaronesia)

Kurzfassung der Dissertation an der Ruprecht-Karls-Universität Heidelberg, Fakultät für Biowissenschaften, betreut durch Prof. Dr. Michael Wink, Ruprecht-Karls-Universität Heidelberg, Institut für Pharmazie und Molekulare Biotechnologie (IPMB), Abt. Biologi

Acoustic scattering from sand dollars (Dendraster excentricus) : modeling as high aspect ratio oblate objects and comparison to experiment

Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2008Benthic shells can contribute greatly to the scattering variability of the ocean bottom, particularly at low grazing angles. Among the effects of shell aggregates are increased scattering strength and potential subcritical angle penetration of the seafloor. Sand dollars (Dendraster excentricus) occur commonly in the ocean and have been shown to be significant scatters of sound. In order to understand more fully the scattering mechanisms of these organisms, the scattering from individual sand dollars was studied using several methods. Using an approximation to the Helmholtz-Kirchhoff integral, the Kirchhoff method gives an analytic integral expression to the backscattering from an object. This integral was first solved analytically for a disk and a spherical cap, two high aspect ratio oblate shapes which simplify the shape of an individual sand dollar. A method for solving the Kirchhoff integral numerically was then developed. An exact three dimensional model of a sand dollar test was created from computed tomography scans. The Kirchhoff integral was then solved numerically for this model of the sand dollar. The finite element method, a numerical technique for approximating the solutions to partial differential equations and integral equations, was used to model the scattering from an individual sand dollar as well. COMSOL Multiphysics was used for the implementation of the finite element method. Modeling results were compared with published laboratory experimental data from the free field scattering of both an aluminum disk and a sand dollar. Insight on the scattering mechanisms of individual sand dollar, including elastic behavior and diffraction effects, was gained from these comparisons

Rotordynamic coefficients and leakage flow of parallel grooved seals and smooth seals

Based on Childs finite length solution for annular plain seals an extension of the bulk flow theory is derived to calculate the rotordynamic coefficients and the leakage flow of seals with parallel grooves in the stator. Hirs turbulent lubricant equations are modified to account for the different friction factors in circumferential and axial direction. Furthermore an average groove depth is introduced to consider the additional circumferential flow in the grooves. Theoretical and experimental results are compared for the smooth constant clearance seal and the corresponding seal with parallel grooves. Compared to the smooth seal the direct and cross-coupled stiffness coefficients as well as the direct damping coefficients are lower in the grooved seal configuration. Leakage is reduced by the grooving pattern

SnapShot: Tumor evolution

Understanding how tumors grow and evolve over time is crucial to help shed light on the underlying reasons why treatments fail and tumors metastasize. This SnapShot provides a brief introduction into the main concepts of tumor evolution

Instantaneous PSD Estimation for Speech Enhancement based on Generalized Principal Components

Power spectral density (PSD) estimates of various microphone signal components are essential to many speech enhancement procedures. As speech is highly non-nonstationary, performance improvements may be gained by maintaining time-variations in PSD estimates. In this paper, we propose an instantaneous PSD estimation approach based on generalized principal components. Similarly to other eigenspace-based PSD estimation approaches, we rely on recursive averaging in order to obtain a microphone signal correlation matrix estimate to be decomposed. However, instead of estimating the PSDs directly from the temporally smooth generalized eigenvalues of this matrix, yielding temporally smooth PSD estimates, we propose to estimate the PSDs from newly defined instantaneous generalized eigenvalues, yielding instantaneous PSD estimates. The instantaneous generalized eigenvalues are defined from the generalized principal components, i.e. a generalized eigenvector-based transform of the microphone signals. We further show that the smooth generalized eigenvalues can be understood as a recursive average of the instantaneous generalized eigenvalues. Simulation results comparing the multi-channel Wiener filter (MWF) with smooth and instantaneous PSD estimates indicate better speech enhancement performance for the latter. A MATLAB implementation is available online

Qualifikationsfrüherkennung und Beratung: Organisationsberater als Grenzgänger zwischen Berufsbildungssystem und Unternehmen

Ein Schwerpunkt der Diskussionen zur Entwicklung und Etablierung der Früherkennungsforschung ist die Frage nach geeigneten Erkenntnis- und Forschungszugängen, um auf veränderte Kompetenz- und Qualifikationserfordernisse rechtzeitig, möglichst in einem status nascendi aufmerksam zu werden. In Deutschland besteht seit den 1990er Jahren eine Früherkennungsforschung, durch die veränderte Arbeitsanforderungen und ihre Folgen für die Kompetenzen und Qualifikationen möglichst frühzeitig wahrgenommen und systematisch untersucht werden. Erkenntnisse der Früherkennungsforschung sollen der Innovationsförderung und der Modernisierung der Berufsbildung dienen und insbesondere dazu beitragen, neue Qualifikationsprofile zu entwickeln und bestehende Qualifikationsstandards zu reformieren. Mit dem im vorliegenden Beitrag vorgestellten Forschungsansatz wird die Expertise von Organisationsberatern für die Qualifikationsfrüherkennung erschlossen. Die empirischen Ergebnisse eines Forschungsprojekts am Bundesinstitut für Berufsbildung (BIBB) zum Erfahrungswissen von Beratern zeigen, dass diese als 'Grenzgänger des betrieblichen Geschehens' einen privilegierten Zugang zum Qualifikationsbedarf von Unternehmen haben. Der Beitrag thematisiert die besondere Bedeutung des Beraterwissens für Früherkennung und Qualifikationsforschung und plädiert für eine weitere Nutzung dieser Expertise. (ICA2

Funktionelle Charakterisierung IRF4-gesteuerter Transkriptionsfaktorkomplexe in Th9-Zellen

IRF4 ist ein Transkriptionsfaktor, der für die Differenzierung von Th9-Zellen essenziell ist und durch Bindung an den Il9-Promotor die Produktion des Th9-typischen Zytokins IL-9 aktiviert. Da IL-9 die Entstehung allergischer Erkrankungen begünstigen kann, entwickeln Irf4-defiziente Tiere im Vergleich zu Wildtyp-Tieren aufgrund einer geringeren IL-9-Expression deutlich schwächere Symptome bei allergischem Asthma. Im Rahmen dieser Arbeit wurden Biotin-vermittelte Affinitätsreinigungen etabliert und angewandt, um IRF4 im Hinblick auf seine transkriptionelle Funktion zu untersuchen. Hierfür wurde eigens eine Mauslinie generiert, die ubiquitär die in vivo Biotinylierung von IRF4 ermöglicht. Der Vorteil dieser Methoden gegenüber herkömmlichen Immunpräzipitationen besteht darin, dass Streptavidin anstelle von spezifischen Antikörpern zur Isolation des biotinylierten IRF4 in Komplex mit interagierenden Proteinen oder gebundener DNA genutzt werden kann. Im Anschluss an eine Biotin-vermittelte IRF4-Interaktompräzipitation wurden die isolierten Proteine via Western Blot und Massenspektrometrie analysiert. Dabei konnten 137 IRF4-interagierende Proteine identifiziert werden, von denen ein Großteil an der transkriptionellen Regulation von Genen des Immunsystems beteiligt ist. Mithilfe einer Literatur-basierten Datenanalyse wurden IRF4-Interaktionspartner wie IKZF1/3, EZH2 und TYY2 identifiziert, die für weitere Untersuchungen zur Charakterisierung von IRF4-gesteuerten Transkriptionsfaktorkomplexen von hohem Interesse sind. Durch eine Biotin-vermittelte Chromatin-Immunpräzipitation („bioChIP“) mit anschließender Sequenzierung erfolgte eine genomweite Identifizierung von IRF4-Bindestellen in Th9-Zellen. Die Ergebnisse zeigten, dass IRF4 nicht nur am Il9-Promotor eine regulatorische Rolle spielt, sondern durch die Bindung an den Transkriptionsstartpunkt verschiedener Gene des adaptiven Immunsystems sehr wahrscheinlich auch Einfluss auf deren Expression nimmt. Auch hier rückte eine Literatur-basierte Datenanalyse mehrere Gene wie z.B. Prdm-1, Foxo1 und Gene des JAK-STAT-Signalwegs in den Fokus für weiterführende, experimentelle Untersuchungen zur IRF4-regulierten Transkription. Es zeichnet sich ein komplexes, IRF4-gesteuertes transkriptionsregulatorisches Netzwerk ab, in dem IRF4 – in Abhängigkeit seiner Interaktionspartner sowie der jeweils spezifischen DNA-Bindestellen – sowohl als Aktivator als auch Repressor agieren kann. Außerdem scheinen mehrere sich selbst regulierende Reaktionen und verstärkende Rückkopplungsschleifen zu existieren. Abschließend bleibt zu sagen, dass IRF4 nicht nur für die Differenzierung und IL-9-Produktion von Th9-Zellen eine Rolle spielt, sondern an zahlreichen Reaktionen des Immunsystems beteiligt ist. Zukünftige Studien zur Modulation der IRF4-gesteuerten Transkription ermöglichen die Entwicklung neuer Strategien, die potenziell für immuntherapeutische Maßnahmen (z.B. bei Asthma) eingesetzt werden können.IRF4 is a transcription factor essential for Th9-development and production of the Th9-cell specific cytokine IL-9 through transactivation of the Il9-promoter. IL-9 promotes the development of allergic diseases. Accordingly, it has been demonstrated that Irf4-deficient mice develop less symptoms of allergic asthma due to an impaired IL-9-production. In this project, biotin-dependent affinity maturations were optimized to characterize the transcriptional role of IRF4. To do so, a mouse model was established that allows the in vivo biotinylation of IRF4. One major advantage of this method over conventional immunoprecipitations is the use of streptavidin instead of specific antibodies to isolate the biotinylated transcription factor together with interacting proteins or bound DNA. Following a biotin-dependent IRF4-pulldown, the isolated proteins were analyzed via Western Blot and mass spectrometry. Thereby, 137 proteins could be identified, the majority of which function in the transcriptional regulation of genes playing a role in immunity. Through a literature-base data analysis IRF4-interaction partners such as IKZF1/3, EZH2 and TYY2 could be determined, which are of great interest to further characterize IRF4-dependent transcription factor complexes. A biotin-dependent Chromatin-Immunoprecipitation (“bioChIP”) and subsequent sequencing led to the genome wide identification of IRF4-bound genes in Th9-cells. Analysis of these data showed that IRF4 not only plays a regulatory role at the Il9-promoter but might also impact the expression of various other genes participating in the adaptive immune system by binding the respective transcription start site (TSS). Again, a literature-based data evaluation highlighted genes like Prdm-1, Foxo1 and genes of the JAK-STAT-signaling pathway for further investigation of IRF4-dependent transcription. Combined, these results suggest a complex IRF4-regulated transcriptional network in which IRF4 – depending on its interaction partners as well as its DNA-binding site – can act as both transcriptional activator and repressor. Furthermore, several self-regulating reactions and positive feedback loops seem to exist. To conclude, IRF4 does not only play an important role in the differentiation and the IL-9-production of Th9-cells but is also involved in multiple immune reactions. Future studies concerning the modulation of the IRF4-dependent transcriptional network will allow for the development of new strategies that potentially utilize immunotherapeutic approaches (e.g. in allergic asthma)

Low-Complexity Steered Response Power Mapping based on Nyquist-Shannon Sampling

The steered response power (SRP) approach to acoustic source localization computes a map of the acoustic scene from the frequency-weighted output power of a beamformer steered towards a set of candidate locations. Equivalently, SRP may be expressed in terms of time-domain generalized cross-correlations (GCCs) at lags equal to the candidate locations' time-differences of arrival (TDOAs). Due to the dense grid of candidate locations, each of which requires inverse Fourier transform (IFT) evaluations, conventional SRP exhibits a high computational complexity. In this paper, we propose a low-complexity SRP approach based on Nyquist-Shannon sampling. Noting that on the one hand the range of possible TDOAs is physically bounded, while on the other hand the GCCs are bandlimited, we critically sample the GCCs around their TDOA interval and approximate the SRP map by interpolation. In usual setups, the number of sample points can be orders of magnitude less than the number of candidate locations and frequency bins, yielding a significant reduction of IFT computations at a limited interpolation cost. Simulations comparing the proposed approximation with conventional SRP indicate low approximation errors and equal localization performance. MATLAB and Python implementations are available online