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Search Results: 1 - 10 of 405145 matches for " Oliver M. Sieber "
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Spectral proper orthogonal decomposition
Moritz Sieber,Kilian Oberleithner,Christian Oliver Paschereit
Physics , 2015,
Abstract: The identification of coherent structures from experimental or numerical data is an essential task when conducting research in fluid dynamics. This typically involves the construction of an empirical mode base that appropriately captures the dominant flow structures. The most prominent candidates are the energy-ranked proper orthogonal decomposition (POD) and the frequency ranked Fourier decomposition and dynamic mode decomposition (DMD). However, these methods fail when the relevant coherent structures occur at low energies or at multiple frequencies, which is often the case. To overcome the deficit of these "rigid" approaches, we propose a new method termed Spectral Proper Orthogonal Decomposition (SPOD). It is based on classical POD and it can be applied to spatially and temporally resolved data. The new method involves an additional temporal constraint that enables a clear separation of phenomena that occur at multiple frequencies and energies. SPOD allows for a continuous shifting from the energetically optimal POD to the spectrally pure Fourier decomposition by changing a single parameter. In this article, SPOD is motivated from phenomenological considerations of the POD autocorrelation matrix and justified from dynamical system theory. The new method is further applied to three sets of PIV measurements of flows from very different engineering problems. We consider the flow of a swirl-stabilized combustor, the wake of an airfoil with a Gurney flap, and the flow field of the sweeping jet behind a fluidic oscillator. For these examples, the commonly used methods fail to assign the relevant coherent structures to single modes. The SPOD, however, achieves a proper separation of spatially and temporally coherent structures, which are either hidden in stochastic turbulent fluctuations or spread over a wide frequency range.
Universality in quantum parametric correlations
P. Leboeuf,M. Sieber
Physics , 1999, DOI: 10.1103/PhysRevE.60.3969
Abstract: We investigate the universality of correlation functions of chaotic and disordered quantum systems as an external parameter is varied. A new, general scaling procedure is introduced which makes the theory invariant under reparametrizations. Under certain general conditions we show that this procedure is unique. The approach is illustrated with the particular case of the distribution of eigenvalue curvatures. We also derive a semiclassical formula for the non-universal scaling factor, and give an explicit expression valid for arbitrary deformations of a billiard system.
Modification of Membrane Fluidity by Gravity  [PDF]
Michaela Sieber, Wolfgang Hanke, Florian P. M. Kohn
Open Journal of Biophysics (OJBIPHY) , 2014, DOI: 10.4236/ojbiphy.2014.44012
Abstract: Biological membranes are preferentially composed of lipids and proteins, and it is assumed that mainly the proteins are responsible for their functional properties. Nevertheless, during the last years, the contribution of the plain lipid matrix and its physico-chemical parameters to membrane functionality has been shown to be of high relevance. This is also correct for the gravity dependence of cells and organisms which is well accepted since long for a wide range of biological systems. Thus, the question must be asked, whether, and how far plain lipid membranes are affected by gravity directly. In this study we show that the fluidity (viscosity) of plain lipid membranes, as well as that of cell membranes, is gravity dependent, using a multipurpose 96-well plate reader in the fluorescence polarization anisotropy mode in a parabolic flight mission. Plain lipid vesicles and cells from a human cancer cell line have been used in these experiments. Necessarily, membrane-integrated proteins should be affected by this in their function. As a consequence any living cell will be able to sense at least basically gravity.
Conductance and Capacity of Plain Lipid Membranes under Conditions of Variable Gravity  [PDF]
Michaela Sieber, Stefan Kaltenbach, Wolfgang Hanke, Florian P. M. Kohn
Journal of Biomedical Science and Engineering (JBiSE) , 2016, DOI: 10.4236/jbise.2016.98031
Abstract: Biological cell membranes are complex structures containing mainly lipids and proteins. Functional aspects of such membranes are usually attributed to membrane integral proteins. However, it is well established that parameters of the lipid matrix are modifying the function of proteins. Additionally, electrical capacity and conductance of the plain lipid matrix of membranes are contributing directly to cellular functions as there is, for example, the propagation of action potentials. Accordingly the dependence of these parameters on changes of gravity might be important in the field of life sciences under space conditions. In this study consequently we have performed experiments in parabolic flight campaigns utilizing the patch-clamp technology to investigate conductance and capacity of plain lipid vesicle membranes under conditions of changing gravity. Both capacity and conductance were found to be gravity dependent. The changes in capacity could be contributed to changes in membrane geometry. Significant permeability in plain lipid membranes could be only observed at high potentials, where spontaneous current fluctuations occurred. The probability of these fluctuations was gravity dependent.
Widespread FRA1-Dependent Control of Mesenchymal Transdifferentiation Programs in Colorectal Cancer Cells
Jeannine Diesch, Elaine Sanij, Omer Gilan, Christopher Love, Hoanh Tran, Nicholas I. Fleming, Jason Ellul, Marcia Amalia, Izhak Haviv, Richard B. Pearson, Eugene Tulchinsky, John M. Mariadason, Oliver M. Sieber, Ross D. Hannan, Amardeep S. Dhillon
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0088950
Abstract: Tumor invasion and metastasis involves complex remodeling of gene expression programs governing epithelial homeostasis. Mutational activation of the RAS-ERK is a frequent occurrence in many cancers and has been shown to drive overexpression of the AP-1 family transcription factor FRA1, a potent regulator of migration and invasion in a variety of tumor cell types. However, the nature of FRA1 transcriptional targets and the molecular pathways through which they promote tumor progression remain poorly understood. We found that FRA1 was strongly expressed in tumor cells at the invasive front of human colorectal cancers (CRCs), and that its depletion suppressed mesenchymal-like features in CRC cells in vitro. Genome-wide analysis of FRA1 chromatin occupancy and transcriptional regulation identified epithelial-mesenchymal transition (EMT)-related genes as a major class of direct FRA1 targets in CRC cells. Expression of the pro-mesenchymal subset of these genes predicted adverse outcomes in CRC patients, and involved FRA-1-dependent regulation and cooperation with TGFβ signaling pathway. Our findings reveal an unexpectedly widespread and direct role for FRA1 in control of epithelial-mesenchymal plasticity in CRC cells, and suggest that FRA1 plays an important role in mediating cross talk between oncogenic RAS-ERK and TGFβ signaling networks during tumor progression.
Semiclassical Interpretation of the Mass Asymmetry in Nuclear Fission
M. Brack,S. M. Reimann,M. Sieber
Physics , 1997, DOI: 10.1103/PhysRevLett.79.1817
Abstract: We give a semiclassical interpretation of the mass asymmetry in the fission of heavy nuclei. Using only a few classical periodic orbits and a cavity model for the nuclear mean field, we reproduce the onset of left-right asymmetric shapes at the fission isomer minimum and the correct topology of the deformation energy surface in the region of the outer fission barrier. We point at the correspondence of the single-particle quantum states responsible for the asymmetry with the leading classical orbits, both lying in similar equatorial planes perpendicular to the symmetry axis of the system.
Wavefunction localization and its semiclassical description in a 3-dimensional system with mixed classical dynamics
M. Brack,M. Sieber,S. M. Reimann
Physics , 2000, DOI: 10.1238/Physica.Topical.090a00146
Abstract: We discuss the localization of wavefunctions along planes containing the shortest periodic orbits in a three-dimensional billiard system with axial symmetry. This model mimicks the self-consistent mean field of a heavy nucleus at deformations that occur characteristically during the fission process [1,2]. Many actinide nuclei become unstable against left-right asymmetric deformations, which results in asymmetric fragment mass distributions. Recently we have shown [3,4] that the onset of this asymmetry can be explained in the semiclassical periodic orbit theory by a few short periodic orbits lying in planes perpendicular to the symmetry axis. Presently we show that these orbits are surrounded by small islands of stability in an otherwise chaotic phase space, and that the wavefunctions of the diabatic quantum states that are most sensitive to the left-right asymmetry have their extrema in the same planes. An EBK quantization of the classical motion near these planes reproduces the exact eigenenergies of the diabatic quantum states surprisingly well.
Climate tipping as a noisy bifurcation: a predictive technique
J. M. T. Thompson,Jan Sieber
Physics , 2010, DOI: 10.1093/imamat/hxq060
Abstract: It is often known, from modelling studies, that a certain mode of climate tipping (of the oceanic thermohaline circulation, for example) is governed by an underlying fold bifurcation. For such a case we present a scheme of analysis that determines the best stochastic fit to the existing data. This provides the evolution rate of the effective control parameter, the variation of the stability coefficient, the path itself and its tipping point. By assessing the actual effective level of noise in the available time series, we are then able to make probability estimates of the time of tipping. This new technique is applied, first, to the output of a computer simulation for the end of greenhouse Earth about 34 million years ago when the climate tipped from a tropical state into an icehouse state with ice caps. Second, we use the algorithms to give probabilistic tipping estimates for the end of the most recent glaciation of the Earth using actual archaeological ice-core data.
Semiclassical approach to discrete symmetries in quantum chaos
Chris Joyner,Sebastian Müller,Martin Sieber
Physics , 2012, DOI: 10.1088/1751-8113/45/20/205102
Abstract: We use semiclassical methods to evaluate the spectral two-point correlation function of quantum chaotic systems with discrete geometrical symmetries. The energy spectra of these systems can be divided into subspectra that are associated to irreducible representations of the corresponding symmetry group. We show that for (spinless) time reversal invariant systems the statistics inside these subspectra depend on the type of irreducible representation. For real representations the spectral statistics agree with those of the Gaussian Orthogonal Ensemble (GOE) of Random Matrix Theory (RMT), whereas complex representations correspond to the Gaussian Unitary Ensemble (GUE). For systems without time reversal invariance all subspectra show GUE statistics. There are no correlations between non-degenerate subspectra. Our techniques generalize recent developments in the semiclassical approach to quantum chaos allowing one to obtain full agreement with the two-point correlation function predicted by RMT, including oscillatory contributions.
Functional Screening Identifies miRNAs Influencing Apoptosis and Proliferation in Colorectal Cancer
Lise Lotte Christensen, Anja Holm, Juha Rantala, Olli Kallioniemi, Mads H. Rasmussen, Marie S. Ostenfeld, Frederik Dagnaes-Hansen, Bodil ?ster, Troels Schepeler, Heidi Tobiasen, Kasper Thorsen, Oliver M. Sieber, Peter Gibbs, Philippe Lamy, Torben F. Hansen, Anders Jakobsen, Eva M. Riising, Kristian Helin, Jan Lubinski, Rikke Hagemann-Madsen, S?ren Laurberg, Torben F. ?rntoft, Claus L. Andersen
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0096767
Abstract: MicroRNAs (miRNAs) play a critical role in many biological processes and are aberrantly expressed in human cancers. Particular miRNAs function either as tumor suppressors or oncogenes and appear to have diagnostic and prognostic significance. Although numerous miRNAs are dys-regulated in colorectal cancer (CRC) only a small fraction has been characterized functionally. Using high-throughput functional screening and miRNA profiling of clinical samples the present study aims at identifying miRNAs important for the control of cellular growth and/or apoptosis in CRC. The high-throughput functional screening was carried out in six CRC cell lines transfected with a pre-miR library including 319 synthetic human pre-miRs. Phenotypic alterations were evaluated by immunostaining of cleaved cPARP (apoptosis) or MKI67 (proliferation). Additionally, TaqMan Human MicroRNA Array Set v2.0 was used to profile the expression of 667 miRNAs in 14 normal colon mucosa and 46 microsatellite stable stage II CRC patients. Among the miRNAs that induced growth arrest and apoptosis in the CRC cell lines, and at same time were dys-regulated in the clinical samples, miR-375 was selected for further analysis. Independent in vitro analysis of transient and stable transfected CRC cell lines confirmed that miR-375 reduces cell viability through the induction of apoptotic death. We identified YAP1 as a direct miR-375 target in CRC and show that HELLS and NOLC1 are down-stream targets. Knock-down of YAP1 mimicked the phenotype induced by miR-375 over-expression indicating that miR-375 most likely exerts its pro-apoptotic role through YAP1 and its anti-apoptotic down-stream targets BIRC5 and BCL2L1. Finally, in vivo analysis of mouse xenograft tumors showed that miR-375 expression significantly reduced tumor growth. We conclude that the high-throughput screening successfully identified miRNAs that induce apoptosis and/or inhibit proliferation in CRC cells. Finally, combining the functional screening with profiling of CRC tissue samples we identified clinically relevant miRNAs and miRNA targets in CRC.
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