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Search Results: 1 - 10 of 4897 matches for " Wolfgang Bohn "
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Nestin Modulates Glucocorticoid Receptor Function by Cytoplasmic Anchoring
Rudolph Reimer, Heike Helmbold, Beata Szalay, Christian Hagel, Heinrich Hohenberg, Wolfgang Deppert, Wolfgang Bohn
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0006084
Abstract: Nestin is the characteristic intermediate filament (IF) protein of rapidly proliferating progenitor cells and regenerating tissue. Nestin copolymerizes with class III IF-proteins, mostly vimentin, into heteromeric filaments. Its expression is downregulated with differentiation. Here we show that a strong nestin expression in mouse embryo tissue coincides with a strong accumulation of the glucocorticoid receptor (GR), a key regulator of growth and differentiation in embryonic development. Microscopic studies on cultured cells show an association of GR with IFs composed of vimentin and nestin. Cells lacking nestin, but expressing vimentin, or cells expressing vimentin, but lacking nestin accumulate GR in the nucleus. Completing these networks with an exogenous nestin, respectively an exogenous vimentin restores cytoplasmic anchoring of GR to the IF system. Thus, heteromeric filaments provide the basis for anchoring of GR. The reaction pattern with phospho-GR specific antibodies and the presence of the chaperone HSC70 suggest that specifically the unliganded receptor is anchored to the IF system. Ligand addition releases GR from IFs and shifts the receptor into the nucleus. Suppression of nestin by specific shRNA abolishes anchoring of GR, induces its accumulation in the nucleus and provokes an irreversible G1/S cell cycle arrest. Suppression of GR prior to that of nestin prevents entry into the arrest. The data give evidence that nestin/vimentin specific anchoring modulates growth suppression by GR. We hypothesize that expression of nestin is a major determinant in suppression of anti-proliferative activity of GR in undifferentiated tissue and facilitates activation of this growth control in a precise tissue and differentiation dependent manner.
Soil-Based Biofiltration for Air Purification:Potentials for Environmental and Space LifeSupport Application  [PDF]
Mark Nelson, Hinrich L. Bohn
Journal of Environmental Protection (JEP) , 2011, DOI: 10.4236/jep.2011.28125
Abstract: Soil biofiltration, also known as soil bed reactor (SBR), technology was originally developed in Germany to take advantage of the diversity in microbial mechanisms to control gases producing malodor in industrial processes. The approach has since gained wider international acceptance and continues to see improvements to maximize microbial and process efficiency and extend the range of problematical gases for which the technology can be an effective control. We review the basic mechanisms which underlay microbial soil processes involved in air purification, advantages and limitations of the technology and the current research status of the approach. Soil biofiltration has lower capital and operating/energetic costs than conventional technologies and is well adapted to handle contaminants in moderate concentrations. The systems can be engineered to optimize efficiency though manipulation of temperature, pH, moisture content, soil organic matter and airflow rates. Soil air biofiltration technology was modified for application in the Biosphere 2 project, which demonstrated in preparatory research with a number of closed system testbeds that soil could also support crop plants while also serving as soil filters with airpumps to push air through the soil. This Biosphere 2 research demonstrated in several closed system testbeds that a number of important trace gases could be kept under control and led to the engineering of the entire agricultural soil of Biosphere 2 to serve as a soil filtration unit for the facility. Soil biofiltration, coupled with food crop production, as a component of bioregenerative space life support systems has the advantages of lower energy use and avoidance of the consumables required for other air purification approaches. Expanding use of soil biofiltration can aid a number of environmental applications, from the mitigation of indoor air pollution, as a method of reducing global warming impact of methane (biogas), improvement of industrial air emissions and prevention of accidental release of toxic gases.
An introduction to Seiberg-Witten theory on closed 3-manifolds
Michael Bohn
Mathematics , 2007,
Abstract: This is a version of the author's diploma thesis written at the University of Cologne in 2002/03. The topic is the construction of Seiberg-Witten invariants of closed 3-manifolds. In analogy to the four dimensional case, the structure of the moduli space is investigated. The Seiberg-Witten invariants are defined and their behaviour under deformation of the Riemannian metric is analyzed. Since it is essentially an exposition of results which were already known during the time of writing, the thesis has not been published. In particular, the author does not claim any originality concerning the results. Moreover, new developments of the theory are not included. However, the detailed account--together with the appendices on the required functional analytic and geometric background--might be of interest for people starting to work in the area of gauge field theory.
On Rho invariants of fiber bundles
Michael Bohn
Mathematics , 2009,
Abstract: Using adiabatic limits of Eta invariants, Rho invariants of the total space of a fiber bundle are investigated. One concern is to formulate the aspects of local index theory for families of Dirac operator in terms of the odd signature operator, and place known results in a context which permits the treatment of Rho invariants. The main focus is, however, to use this to compute Rho invariants for explicit classes of fibered 3-manifolds. More precisely, we consider $\U(1)$-Rho invariants of principal $S^1$-bundles over closed, oriented surfaces as well as mapping tori with torus fiber. Hyperbolic monodromy maps deserve particular attention. When discussing them, the logarithm of a generalized Dedekind Eta function naturally appears. An explicit formula for $\U(1)$-Rho invariants is then deduced from a transformation formula for these Dedekind Eta functions.
Chromatic polynomials of complementary (n,k)-clique pairs
Adam Bohn
Mathematics , 2010,
Abstract: We introduce a class of pairs of graphs consisting of two cliques joined by an arbitrary number of edges. The members of a pair have the property that the clique-bridging edge-set of one graph is the complement of that of the other. We prove a precise relation between the chromatic polynomials of the graphs in such a pair, showing that they have the same splitting field, and that the number of acyclic orientations of each graph is determined by the number of proper vertex-colourings of the other.
Chromatic polynomials of complements of bipartite graphs
Adam Bohn
Mathematics , 2011,
Abstract: Bicliques are complements of bipartite graphs; as such each consists of two cliques joined by a number of edges. In this paper we study algebraic aspects of the chromatic polynomials of these graphs. We derive a formula for the chromatic polynomial of an arbitrary biclique, and use this to give certain conditions under which two of the graphs have chromatic polynomials with the same splitting field. Finally, we use a subfamily of bicliques to prove the cubic case of the $\alpha +n$ conjecture, by showing that for any cubic integer $\alpha$, there is a natural number $n$ such that $\alpha +n$ is a chromatic root.
A set of chromatic roots which is dense in the complex plane and closed under multiplication by positive integers
Adam Bohn
Mathematics , 2011,
Abstract: We study a very large family of graphs, the members of which comprise disjoint paths of cliques with extremal cliques identified. This broad characterisation naturally generalises those of various smaller families of graphs having well-known chromatic polynomials. We derive a relatively simple formula for an arbitrary member of the subfamily consisting of those graphs whose constituent clique-paths have at least one trivial extremal clique, and use this formula to show that the set of all non-integer chromatic roots of these graphs is closed under multiplication by natural numbers. A well-known result of Sokal then leads to our main result, which is that there exists a set of chromatic roots which is closed under positive integer multiplication in addition to being dense in the complex plane. Our findings lend considerable weight to a conjecture of Cameron, who has suggested that this closure property may be a generic feature of the chromatic polynomial. We also hope that the formula we provide will be of use to those computing with chromatic polynomials.
The slippage paradox
Steffen Bohn
Quantitative Finance , 2011,
Abstract: Buying or selling assets leads to transaction costs for the investor. On one hand, it is well know to all market practionaires that the transaction costs are positive on average and present therefore systematic loss. On the other hand, for every trade, there is a buy side and a sell side, the total amount of asset and the total amount of cash is conserved. I show, that the apparently paradoxical observation of systematic loss of all participants is intrinsic to the trading process since it corresponds to a correlation of outstanding orders and price changes.
Exogenous Antioxidants—Double-Edged Swords in Cellular Redox State: Health Beneficial Effects at Physiologic Doses versus Deleterious Effects at High Doses
Jaouad Bouayed,Torsten Bohn
Oxidative Medicine and Cellular Longevity , 2010, DOI: 10.4161/oxim.3.4.12858
Abstract: The balance between oxidation and antioxidation is believed to be critical in maintaining healthy biological systems. Under physiological conditions, the human antioxidative defense system including e.g., superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione (GSH) and others, allows the elimination of excess reactive oxygen species (ROS) including, among others superoxide anions (O2.-), hydroxyl radicals (OH.), alkoxyl radicals (RO.) and peroxyradicals (ROO.). However, our endogenous antioxidant defense systems are incomplete without exogenous originating reducing compounds such as vitamin C, vitamin E, carotenoids and polyphenols, playing an essential role in many antioxidant mechanisms in living organisms. Therefore, there is continuous demand for exogenous antioxidants in order to prevent oxidative stress, representing a disequilibrium redox state in favor of oxidation. However, high doses of isolated compounds may be toxic, owing to prooxidative effects at high concentrations or their potential to react with beneficial concentrations of ROS normally present at physiological conditions that are required for optimal cellular functioning. This review aims to examine the double-edged effects of dietary originating antioxidants with a focus on the most abundant compounds, especially polyphenols, vitamin C, vitamin E and carotenoids. Different approaches to enrich our body with exogenous antioxidants such as via synthetic antioxidants, diets rich in fruits and vegetables and taking supplements will be reviewed and experimental and epidemiological evidences discussed, highlighting that antioxidants at physiological doses are generally safe, exhibiting interesting health beneficial effects.
Manuten??o parenteral de líquidos na crian?a agudamente doente
Choong, Karen;Bohn, Desmond;
Jornal de Pediatria , 2007, DOI: 10.1590/S0021-75572007000300002
Abstract: objective: to examine electrolyte-free water requirements that should be considered when administering maintenance fluids in a critically ill child. we examine some of the difficulties in estimating these requirements, and discuss the controversies with respect to the traditional recommendations. sources: medline (1966-2007), embase (1980-2007), and the cochrane library, using the terms: “fluid therapy”, “hypotonic”, “isotonic solution”, and synonyms or related terms. summary of the findings: the ideal maintenance solution and fluid regimen remains a topic of heated debate in pediatrics. the traditional recommendations for maintenance fluids are increasingly criticized as they do not consistently apply in acute illness, where energy expenditure and electrolyte requirements deviate significantly from the original estimates. a physiologically based framework for prescribing maintenance fluids is presented, with the objective of maintaining tonicity balance, and infusing the minimum volume of maintenance fluid required to maintain hemodynamics. indications for isotonic and hypotonic solutions are discussed. conclusions: maintenance fluid prescriptions should be individualized. no single intravenous solution is ideal for every child during all phases of illness, but there is evidence to suggest that the safest empirical choice is an isotonic solution. hypotonic solutions should only be considered if the goal is to achieve a positive free-water balance. critically ill children may require a reduction by as much as 40-50% of the currently recommended maintenance volumes. all patients receiving intravenous fluids should be monitored closely with daily weights, fluid balances, biochemical and clinical parameters in order to best guide this therapy.
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