Optimierung und Validierung eines ex-vivo Kultursystems für trabekulären Knochen

In dieser Arbeit wurde mit dem ZETOS System, einem neuen ex-vivo Kutursystem für trabekulären Knochen gearbeitet. Hauptziel der Arbeit war die Bestimmung der Flussrate in dem ZETOS System, bei der eine optimale physiologische Umgebung für das Wachstum explantierter Knochen gegeben ist. Bei den Untersuchungen stellte sich überraschenderweise heraus, dass die Knochen im experimentellen Ansatz nicht perfundiert werden, sondern der Stofftransport über Diffusion gesteuert wird. Dieser Befund wurde durch Einsatz eines axialen Flusssystems bei gleichem hydrostatischen Druck und durch Diffusionsversuche bestätigt. Das ZETOS System wirkt folglich eher als ein Zirkumfusionssystem als ein Perfusionssystem. Bei der Austestung der beiden Kulturmedien DMEM und BGJb zeigte sich über 26 Kulturtage hinweg, dass BGJb eine Aktivierung von Osteoblasten unabhängig von der angelegten mechanischen Belastung der Knochen induziert. Dies wird in einem Anstieg der relativen Osteoidfläche mit und ohne Belastung sichtbar. In DMEM tritt dagegen keine Veränderung in der relativen Osteoidfläche im Vergleich zum unkultivierten Knochen auf. Bei belasteten und unbelasteten Knochen sind in dem experimentellen Ansatz keine Steifigkeitsveränderungen messbar. Die Analyse der Schnittoberflächen legt den Verdacht nahe, dass eine optimale Kraftübertragung auf den Knochen zu dessen Stimulation nicht gewährleistet war und verbessert werden muss. An Hand der histologischen Beurteilung der Schnitte zeigten sich nach 26- tägiger Kulturdauer keine Anhaltspunkte für einen Vitalitätsverlust der Zellen in dem Kultursystem. Dennoch führten Doppelmarkierungen mit Fluorochromen nur in einer geringen Anzahl der Versuchsansätze zu einer erfolgreichen Messung derWachstumsgeschwindigkeit,die sich in diesen Fällen allerdings im Rahmen der physiologischen Grundwachstumsgeschwindigkeit bewegt. Um die Vitalität der Knochen eindeutig belegen zu können, wird der Einsatz von Verfahren zur Messung der Protein- und DNS-Synthese für zukünftige Optimierungsansätze empfohlen. Letztlich gelang es, zwei Makros zur pixelbasierten Bildanalyse zu erstellen, welche die histologische Auswertung der Schnitte zur Bestimmung der Mineral Aposition Rate (MAR) sowie der relativen Osteoidfläche (Os.Ar/B.Ar) automatisiert ermöglichen

3'-Phosphoadenosine 5'-Phosphate Accumulation Delays the Circadian System.

The circadian system optimizes cellular responses to stress, but the signaling pathways that convey the metabolic consequences of stress into this molecular timekeeping mechanism remain unclear. Redox regulation of the SAL1 phosphatase during abiotic stress initiates a signaling pathway from chloroplast to nucleus by regulating the accumulation of a metabolite, 3'-phosphoadenosine 5'-phosphate (PAP). Consequently, PAP accumulates in response to redox stress and inhibits the activity of exoribonucleases (XRNs) in the nucleus and cytosol. We demonstrated that osmotic stress induces a lengthening of circadian period and that genetically inducing the SAL1-PAP-XRN pathway in plants lacking either SAL1 or XRNs similarly delays the circadian system. Exogenous application of PAP was also sufficient to extend circadian period. Thus, SAL1-PAP-XRN signaling likely regulates circadian rhythms in response to redox stress. Our findings exemplify how two central processes in plants, molecular timekeeping and responses to abiotic stress, can be interlinked to regulate gene expression

A cyclic perspective on transient gust encounters through the lens of persistent homology

Large amplitude gust encounters exhibit a range of separated flow phenomena, making them difficult to characterize using the traditional tools of aerodynamics. In this work, we propose a dynamical systems approach to gust encounters, viewing the flow as a cycle (or a closed trajectory) in state space. We posit that the topology of this cycle, or its shape and structure, provides a compact description of the flow, and can be used to identify coordinates in which the dynamics evolve in a simple, intuitive way. To demonstrate this idea, we consider flowfield measurements of a transverse gust encounter. For each case in the dataset, we characterize the full-state dynamics of the flow using persistent homology, a tool that identifies holes in point cloud data, and transform the dynamics to a reduced-order space using a nonlinear autoencoder. Critically, we constrain the autoencoder such that it preserves topologically relevant features of the original dynamics, or those features identified by persistent homology. Using this approach, we are able to transform six separate gust encounters to a three-dimensional latent space, in which each gust encounter reduces to a simple circle, and from which the original flow can be reconstructed. This result shows that topology can guide the creation of low-dimensional state representations for strong transverse gust encounters, a crucial step toward the modeling and control of airfoil-gust interactions

Discordance between lung function of Chinese university students of 20-year-old established norms

Objective: We examined the validity of the 20-year-old established Asian norms for pulmonary function in a contemporary cohort of Hong Kong Chinese university students. Design and participants: Pulmonary function testing was conducted in university students (n = 805). Setting: A university campus in Hong Kong. Measurements and results: Parameters recorded included gender, age, height, weight, standard lung function variables (ie, FEV1, FVC, and peak expiratory flow rate [PEFR]), and exhaled carbon monoxide (CO) level. Subjects completed a questionnaire on pulmonary health, smoking history, and their dietary and exercise habits within 3 months of the study. Data were compared with the established norms for lung function for Chinese persons from Hong Kong. On average, subjects were taller than those reported in the original cohort, on whom the established norms are based; however, FEV1, FVC, and PEFR were lower. As predicted, the exhaled CO level was higher in smokers. Those who exercised regularly had a higher FEV1 and FVC, and reported fewer respiratory complaints. Conclusions: Our findings support the idea that lung function norms not only differ across ethnic groups, but that they may be susceptible to change over a single generation within an ethnic group living in the same geographic region. Assuming the equivalence of our testing methods and those on which established norms are based, our findings shed further insight into the dynamic nature of lung function, and have implications regarding the definition of normal pulmonary function and its variance over the short term. <br /

Popular Conceptions of Nationhood in Old and New European Member States: Partial Support for the Ethnic-Civic Framework

One of the most influential theories in the study of nationalism has been the ethnic-East/civic-West framework developed by Hans Kohn. Using the 2002 Eurobarometer survey on national identity and building on earlier survey studies, this article examines whether the Kohn framework is valid at the level of popular understandings of nationhood. It scrutinizes the framework both conceptually - do people define nationhood in civic or ethnic terms? - and regionally - is the East indeed more ethnic than the West and the West more civic than the East? It will show that identity markers cluster in a political, a cultural and an ethnic dimension. Respondents do not see these dimensions as competing sources of nationhood, however. The article further lends some support for the regional component of the framework. Lastly, it argues that it is the intensity of national identifications rather than their qualitative nature (ethnic-civic) that correlates with xenophobia. © 2006 Taylor & Francis

Population pulsation resonances of excitons in monolayer MoSe2 with sub 1 {\mu}eV linewidth

Monolayer transition metal dichalcogenides, a new class of atomically thin semiconductors, possess optically coupled 2D valley excitons. The nature of exciton relaxation in these systems is currently poorly understood. Here, we investigate exciton relaxation in monolayer MoSe2 using polarization-resolved coherent nonlinear optical spectroscopy with high spectral resolution. We report strikingly narrow population pulsation resonances with two different characteristic linewidths of 1 {\mu}eV and <0.2 {\mu}eV at low-temperature. These linewidths are more than three orders of magnitude narrower than the photoluminescence and absorption linewidth, and indicate that a component of the exciton relaxation dynamics occurs on timescales longer than 1 ns. The ultra-narrow resonance (<0.2 {\mu}eV) emerges with increasing excitation intensity, and implies the existence of a long-lived state whose lifetime exceeds 6 ns.Comment: (PRL, in press

Smoothed particle hydrodynamics and its applications for multiphase flow and reactive transport in porous media

Smoothed particle hydrodynamics (SPH) is a Lagrangian method based on a meshless discretization of partial differential equations. In this review, we present SPH discretization of the Navier-Stokes and advection-diffusion-reaction equations, implementation of various boundary conditions, and time integration of the SPH equations, and we discuss applications of the SPH method for modeling pore-scale multiphase flows and reactive transport in porous and fractured media.United States. Dept. of Energy. Office of Advanced Scientific Computing Research (Early Career Award, “New Dimension Reduction Methods and Scalable Algorithms for Multiscale Nonlinear Phenomena,” and Collaboratory on Mathematics for Mesoscopic Modeling of Materials (CM4)

Pressure Correction in Density Functional Theory Calculations

First-principles calculations based on density functional theory have been widely used in studies of the structural, thermoelastic, rheological, and electronic properties of earth-forming materials. The exchange-correlation term, however, is implemented based on various approximations, and this is believed to be the main reason for discrepancies between experiments and theoretical predictions. In this work, by using periclase MgO as a prototype system we examine the discrepancies in pressure and Kohn-Sham energy that are due to the choice of the exchange-correlation functional. For instance, we choose local density approximation and generalized gradient approximation. We perform extensive first-principles calculations at various temperatures and volumes and find that the exchange-correlation-based discrepancies in Kohn-Sham energy and pressure should be independent of temperature. This implies that the physical quantities, such as the equation of states, heat capacity, and the Gr\"{u}neisen parameter, estimated by a particular choice of exchange-correlation functional can easily be transformed into those estimated by another exchange-correlation functional. Our findings may be helpful in providing useful constraints on mineral properties %at thermodynamic conditions compatible to deep Earth. at deep Earth thermodynamic conditions