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Search Results: 1 - 10 of 749 matches for " Michaela Sieber "
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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.
Two-dimensional wave patterns of spreading depolarization: retracting, re-entrant, and stationary waves
Markus A. Dahlem,Rudolf Graf,Anthony J. Strong,Jens P. Dreier,Yuliya A. Dahlem,Michaela Sieber,Wolfgang Hanke,Klaus Podoll,Eckehard Schoell
Physics , 2009, DOI: 10.1016/j.physd.2009.08.009
Abstract: We present spatio-temporal characteristics of spreading depolarizations (SD) in two experimental systems: retracting SD wave segments observed with intrinsic optical signals in chicken retina, and spontaneously occurring re-entrant SD waves that repeatedly spread across gyrencephalic feline cortex observed by laser speckle flowmetry. A mathematical framework of reaction-diffusion systems with augmented transmission capabilities is developed to explain the emergence and transitions between these patterns. Our prediction is that the observed patterns are reaction-diffusion patterns controlled and modulated by weak nonlocal coupling. The described spatio-temporal characteristics of SD are of important clinical relevance under conditions of migraine and stroke. In stroke, the emergence of re-entrant SD waves is believed to worsen outcome. In migraine, retracting SD wave segments cause neurological symptoms and transitions to stationary SD wave patterns may cause persistent symptoms without evidence from noninvasive imaging of infarction.
Limites do direito penal: princípios e desafios do novo programa de pesquisa em direito penal no Instituto Max-Planck de direito penal estrangeiro e internacional
Sieber, Ulrich;
Revista Direito GV , 2008, DOI: 10.1590/S1808-24322008000100012
Abstract: this paper describes the research program implemented by the current director of the max-planck-institute for foreign and international penal law, which has its focus directed to the current challenges posed to penal law by contemporary social, economic and political changes. this program has three goals: (i) to analyze the real alterations to security risks and the ideas regarding security in a society branded by globalization and technical, economic and political changes; (ii) to analyze and critically evaluate the legal changes that accompany said changes and their causes; (iii) the development of new answers to the challenges posed to law enforcement policies. in this context, the following aspects are highlighted: international organized criminality, terrorism and crimes committed over the internet.
Sandra Witte: Zouber. Hamburg: Verlag Dr. Kova 2007
Andrea Sieber
querelles-net , 2009,
Abstract: Die Freiburger Dissertation widmet sich dem Faszinosum Magie am Beispiel der h fischen Literatur des 12. und 13. Jahrhunderts. Im Zentrum steht die deskriptive Analyse von Magiedarstellungen auf der Handlungsebene fiktionaler Texte, wobei ein besonderes Augenmerk auf Geschlechterdifferenzen magiekundiger Figuren liegt. Vorab werden m gliche Schnittfl chen zu zeitgen ssischen Diskursen in den Bereichen Religion, Wissenschaft und Heilkunde konturiert und diese um Skizzen zu ausgew hlten nichtfiktionalen Quellen erg nzt. Leider verschenkt die medi vistische Studie durch ihren überwiegend nacherz hlenden Duktus das in der Magie-Thematik inh rente gender-theoretische und kulturwissenschaftliche Potential. This Freiburger dissertation approaches fascination with magic using the example of the courtly literature of the 12th and 13th centuries. Central to the study is the descriptive analysis of representations of magic at the plot level of fictional texts, whereby specific attention is paid to gender differences of those figures skilled in magic. Possible intersections with contemporary discourses in the areas of religion, science, and medical science are outlined at the outset. These are expanded with sketches of select non-fictional sources. Unfortunately, because of its tendency to uncritically re-narrate the texts, the medieval study passes up on the gender-theoretical and cultural studies oriented potential inherent to the theme of magic.
Ern hrung - Ein wichtiger Teil der Therapie
Sieber W
Journal für Ern?hrungsmedizin , 2010,
Abstract:
Semiclassical Transition from an Elliptical to an Oval Billiard
Martin Sieber
Physics , 1996, DOI: 10.1088/0305-4470/30/13/011
Abstract: Semiclassical approximations often involve the use of stationary phase approximations. This method can be applied when $\hbar$ is small in comparison to relevant actions or action differences in the corresponding classical system. In many situations, however, action differences can be arbitrarily small and then uniform approximations are more appropriate. In the present paper we examine different uniform approximations for describing the spectra of integrable systems and systems with mixed phase space. This is done on the example of two billiard systems, an elliptical billiard and a deformation of it, an oval billiard. We derive a trace formula for the ellipse which involves a uniform approximation for the Maslov phases near the separatrix, and a uniform approximation for tori of periodic orbits close to a bifurcation. We then examine how the trace formula is modified when the ellipse is deformed into an oval. This involves uniform approximations for the break-up of tori and uniform approximations for bifurcations of periodic orbits. Relations between different uniform approximations are discussed.
Spectral statistics in chaotic systems with a point interaction
Martin Sieber
Physics , 2000, DOI: 10.1088/0305-4470/33/36/301
Abstract: We consider quantum systems with a chaotic classical limit that are perturbed by a point-like scatterer. The spectral form factor K(tau) for these systems is evaluated semiclassically in terms of periodic and diffractive orbits. It is shown for order tau^2 and tau^3 that off-diagonal contributions to the form factor which involve diffractive orbits cancel exactly the diagonal contributions from diffractive orbits, implying that the perturbation by the scatterer does not change the spectral statistic. We further show that parametric spectral statistics for these systems are universal for small changes of the strength of the scatterer.
Billiard Systems in Three Dimensions: The Boundary Integral Equation and the Trace Formula
Martin Sieber
Physics , 1997, DOI: 10.1088/0951-7715/11/6/010
Abstract: We derive semiclassical contributions of periodic orbits from a boundary integral equation for three-dimensional billiard systems. We use an iterative method that keeps track of the composition of the stability matrix and the Maslov index as an orbit is traversed. Results are given for isolated periodic orbits and rotationally invariant families of periodic orbits in axially symmetric billiard systems. A practical method for determining the stability matrix and the Maslov index is described.
Reviewing Pulsar Spectra
W. Sieber
Physics , 2002,
Abstract: Problems solved? Pulsar research must be considered - 35 years after the detection of pulsars - a mature science, where the basic questions have been raised and discussed. One would hope that many if not all generic and important problems have found some kind of answer and that scientific work can concentrate now on specific details requiring more in depth investigation. We know, however, that this picture is not true. Even well studied areas did in the past not always lead to a general accepted model and some were investigated at the beginning with enthusiasm but left behind. This paper will concentrate on one narrow topic, pulsar radio spectra. It is the attempt to work out, what features are now generally accepted, but also what features are still in discussion after so many years of pulsar research. In this sense the paper will enlighten in a personal view those aspects which are still under discussion.
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