Bielefeld University

About: Bielefeld University is a education organization based out in Bielefeld, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Population & Quantum chromodynamics. The organization has 10123 authors who have published 26576 publications receiving 728250 citations. The organization is also known as: University of Bielefeld & UNIVERSITAET BIELEFELD.

Incorporating Fluctuations and Dynamics in Self-Consistent Field Theories for Polymer Blends

Abstract: We review various methods to investigate the statics and the dynamics of collective composition fluctuations in dense polymer mixtures within fluctuating-field approaches. The central idea of fluctuating-field theories is to rewrite the partition function of the interacting multi-chain systems in terms of integrals over auxiliary, often complex, fields, which are introduced by means of appropriate Hubbard--Stratonovich transformations. Thermodynamic averages such as the average composition and the structure factor can be expressed exactly as averages of these fields. We discuss different analytical and numerical approaches to studying such a theory: The self-consistent field approach solves the integrals over the fluctuating fields in saddle-point approximation. Generalized random phase approximations allow one to incorporate Gaussian fluctuations around the saddle point. Field theoretical polymer simulations are used to study the statistical mechanics of the full system with Complex Langevin or Monte Carlo methods. Unfortunately, they are hampered by the presence of a sign problem. In a dense system, the latter can be avoided without losing essential physics by invoking a saddle point approximation for the complex field that couples to the total density. This leads to the external potential theory. We investigate the conditions under which this approximation is accurate. Finally, we discuss recent approaches to formulate realistic time evolution equations for such models. The methods are illustrated by two examples: A study of the fluctuation-induced formation of a polymeric microemulsion in a polymer-copolymer mixture and a study of early-stage spinodal decomposition in a binary blend.

Lipid microdomain polarization is required for NADPH oxidase-dependent ROS signaling in Picea meyeri pollen tube tip growth

Abstract: *† SUMMARY The polarization of sterol-enriched lipid microdomains has been linked to morphogenesis and cell movement in diverse cell types. Recent biochemical evidence has confirmed the presence of lipid microdomains in plant cells; however, direct evidence for a functional link between these microdomains and plant cell growth is still lacking. Here, we reported the involvement of lipid microdomains in NADPH oxidase (NOX)-dependent reactive oxygen species (ROS) signaling in Picea meyeri pollen tube growth. Staining with di-4-ANEPPDHQ or filipin revealed that sterol-enriched microdomains were polarized to the growing tip of the pollen tube. Sterol sequestration with filipin disrupted membrane microdomain polarization, depressed tip-based ROS formation, dissipated tip-focused cytosolic Ca 2+ gradient and thereby arrested tip growth. NOX clustered at the growing tip, and corresponded with the ordered membrane domains. Immunoblot analysis and native gel assays demonstrated that NOX was partially associated with detergent-resistant membranes and, furthermore, that NOX in a sterol-dependent fashion depends on membrane microdomains for its enzymatic activity. In addition, in vivo time-lapse imaging revealed the coexistence of a steep tip-high apical ROS gradient and subapical ROS production, highlighting the reported signaling role for ROS in polar cell growth. Our results suggest that the polarization of lipid microdomains to the apical plasma membrane, and the inclusion of NOX into these domains, contribute, at least in part, to the ability to grow in a highly polarized manner to form pollen tubes.

Value of H(0) in the inhomogeneous universe.

Abstract: Local measurements of the Hubble expansion rate are affected by structures like galaxy clusters or voids. Here we present a fully relativistic treatment of this effect, studying how clustering modifies the mean distance- (modulus-)redshift relation and its dispersion in a standard cold dark matter universe with a cosmological constant. The best estimates of the local expansion rate stem from supernova observations at small redshifts (0.01

Monetary and Fiscal Policy Interactions in the Euro Area

Abstract: The problem of monetary and fiscal policy interactions is an important issue for the euro area, since the individual member states of the EMU are responsible for their fiscal policies but monetary policy is pursued by a single monetary authority, the ECB. This paper is concerned with empirical evidence on monetary and fiscal policy interactions in the euro area. We first explore fiscal regimes with a VAR model and find empirical evidence that a non-Ricardian fiscal policy has been pursued in both France and Germany. As an example, we then study how one member state of the EMU, namely, Italy, is responding to the common monetary policy with its fiscal policy and find that Italian fiscal policy seemed to be counteractive to the common monetary policy between 1979 and 1998. In order to study monetary and fiscal policy interactions in a more general way, we explore time-varying interactions by estimating a State-Space model with Markov-switching for some Euro-area countries. There appear to be some regime changes in monetary and fiscal policy interactions in France and Germany, but the interactions between the two policies are not strong. Moreover, the two policies have not been accommodative but counteractive to each other. Finally we explore forward-looking behavior in policy interactions and find that expectations do not seem to have played an important role in the policy designs.

The CRP/FNR family protein Bcam1349 is a c-di-GMP effector that regulates biofilm formation in the respiratory pathogen Burkholderia cenocepacia.

Abstract: Burkholderia cenocepacia is an opportunistic respiratory pathogen that can cause severe infections in immune-compromised individuals and is associated with poor prognosis for patients suffering from cystic fibrosis. The second messenger cyclic diguanosine monophosphate (c-di-GMP) has been shown to control a wide range of functions in bacteria, but little is known about these regulatory mechanisms in B. cenocepacia. Here we investigated the role that c-di-GMP plays in the regulation of biofilm formation and virulence in B. cenocepacia. Elevated intracellular levels of c-di-GMP promoted wrinkly colony, pellicle and biofilm formation in B. cenocepacia. A screen for transposon mutants unable to respond to elevated levels of c-di-GMP led to the identification of the mutant bcam1349 that did not display increased biofilm and pellicle formation with excessive c-di-GMP levels, and displayed a biofilm defect with physiological c-di-GMP levels. The bcam1349 gene is predicted to encode a transcriptional regulator of the CRP/FNR superfamily. Analyses of purified Bcam1349 protein and truncations demonstrated that it binds c-di-GMP in vitro. The Bcam1349 protein was shown to regulate the production of a number of components, including cellulose and fimbriae. It was demonstrated that the Bcam1349 protein binds to the promoter region of the cellulose synthase genes, and that this binding is enhanced by the presence of c-di-GMP. The bcam1349 mutant showed reduced virulence in a Galleria mellonella wax moth larvae infection model. Taken together, these findings suggest that the Bcam1349 protein is a transcriptional regulator that binds c-di-GMP and regulates biofilm formation and virulence in B. cenocepacia in response to the level of c-di-GMP.