Persistence length of semiflexible polymers and bending rigidity renormalization

The persistence length of semiflexible polymers and one-dimensional fluid membranes is obtained from the renormalization of their bending rigidity. The renormalized bending rigidity is calculated using an exact real-space functional renormalization group transformation based on a mapping to the one-dimensional Heisenberg model. The renormalized bending rigidity vanishes exponentially at large length scales and its asymptotic behaviour is used to define the persistence length. For semiflexible polymers, our result agrees with the persistence length obtained using the asymptotic behaviour of tangent correlation functions. Our definition differs from the one commonly used for fluid membranes, which is based on a perturbative renormalization of the bending rigidity.Comment: 7 page

Persistence length of semiflexible polymers and bending rigidity renormalization

The persistence length of semiflexible polymers and one-dimensional fluid membranes is obtained from the renormalization of their bending rigidity. The renormalized bending rigidity is calculated using an exact real-space functional renormalization group transformation based on a mapping to the one-dimensional Heisenberg model. The renormalized bending rigidity vanishes exponentially at large length scales and its asymptotic behaviour is used to define the persistence length. For semiflexible polymers, our result agrees with the persistence length obtained using the asymptotic behaviour of tangent correlation functions. Our definition differs from the one commonly used for fluid membranes, which is based on a perturbative renormalization of the bending rigidity.Comment: 7 page

Structured cooperation in computer based collaborative Learning

Es wird der Frage nachgegangen, inwieweit hochstrukturierte kooperative Lernmethoden zur Förderung computerunterstützten kollaborativen Lernens genutzt werden können. Solche Methoden geben Regeln für das Dialogverhalten vor und haben sich in traditionellen face-to-face-Gruppen bewährt. In einer experimentellen Untersuchung wurde in einem telematischen Setting eine Kooperationsstruktur vorgegeben, die mittels Kommunikationsschnittstelle das Dialogverhalten kooperativer Paare gemäß dem Prinzip des gegenseitigen Erklärens regelt. Teilnehmer waren 30 Studenten verschiedener Fachrichtungen. Es zeigte sich im Vergleich zu einer Kontrollgruppe von ebenfalls 30 Studenten ein geringerer Koordinationsaufwand bei der gemeinsamen Aufgabenbearbeitung und ein effektiveres Dialogverhalten im Sinne eines geringeren Anteils an Aussagen zur Dialogsteuerung. Außerdem ergab sich eine Verbesserung der Problemlöseperformanz und des Wissenserwerbs aufgrund der gemeinsamen Aufgabenbearbeitung. (DIPF/Orig.

NEURAL NETWORK MODELING IN SPORT BIOMECHANICS BASED ON THE EXAMPLE OF SHOT-PUT FLIGHT

In this study, a modeling method based on Multi-Layer-Perceptron neural networks (MLP) is presented, using the example of shot-put flight. This method can be used for rapid construction of models. For performance of shot-put, a physical model based on the shots’ equations of motion is easily designed. In this way, an analysis of the shot-put projectory can be used to illustrate the effectiveness of the neural network modeling method. Using the physical model, release data has been determined and altered with random errors such as those introduced by video analysis. A technique for optimal learning with the neural networks has been developed. The resulting MLP models the shot-put flight successfully. The difference between the model’s predicted distance and the distance reached by the physical model are within 2.5%. In conclusion, this method allows rapid creation of models to solve biomechanical problems and can serve as a useful tool for coaches and athletes

The fibronectin-binding integrins α5β1 and αvβ3 differentially modulate RhoA–GTP loading, organization of cell matrix adhesions, and fibronectin fibrillogenesis

We have studied the formation of different types of cell matrix adhesions in cells that bind to fibronectin via either α5β1 or αvβ3. In both cases, cell adhesion to fibronectin leads to a rapid decrease in RhoA activity. However, α5β1 but not αvβ3 supports high levels of RhoA activity at later stages of cell spreading, which are associated with a translocation of focal contacts to peripheral cell protrusions, recruitment of tensin into fibrillar adhesions, and fibronectin fibrillogenesis. Expression of an activated mutant of RhoA stimulates αvβ3-mediated fibrillogenesis. Despite the fact that α5β1-mediated adhesion to the central cell-binding domain of fibronectin supports activation of RhoA, other regions of fibronectin are required for the development of α5β1-mediated but not αvβ3-mediated focal contacts. Using chimeras of β1 and β3 subunits, we find that the extracellular domain of β1 controls RhoA activity. By expressing both β1 and β3 at high levels, we show that β1-mediated control of the levels of β3 is important for the distribution of focal contacts. Our findings demonstrate that the pattern of fibronectin receptors expressed on a cell dictates the ability of fibronectin to stimulate RhoA-mediated organization of cell matrix adhesions

Intestinal Infection Due to Enteroaggregative Eschevichia coli among Human Immunodeficiency Virus—Infected Persons

To investigate the pathogenic role of enteroaggregative Escherichia coli (EAggEC) among human immunodeficiency virus—infected persons, 111 outpatients with and 68 without diarrhea were evaluated. Examination of stool samples included the HeLa cell adherence assay and an EAggEC polymerase chain reaction (PCR) assay using primers complementary for the plasmid locus CVD432. The pCVD432 genotype, adherence phenotype, and patient characteristics were correlated with occurrence of diarrhea by multivariate analyses. EAggEC PCR and adherence assays were positive in 7 (6%) and 24 (22%) patients with diarrhea and in 1 (1%) and 21 (31%) asymptomatic control patients, respectively. Clinical manifestations associated with EAggEC PCR-positive isolates were nonspecific; EAggEC infections were independent of CD4 lymphocyte counts. Of the pCVD432 genotype, 5 (71%) of 7 were resistant to cotrimoxazole and ampicillin, and 1 strain was resistant to ciprofloxacin. Overall, pCVD432 PCR-positive E. coli was the most prevalent intestinal organism associated with diarrhea. The adherence assay results did not correlate with diarrhe

Production of Toxic Volatile Trimethylbismuth by the Intestinal Microbiota of Mice

The biotransformation of metals and metalloids into their volatile methylated derivatives by microbes growing under anaerobic conditions (e.g., the mammalian intestinal microbiota) plays an important role in spreading these compounds in the environment. In this paper, we could show that the presence of an intact intestinal microbiota of mice provides the conditio sine qua non for the production of these mostly toxic derivatives. To document the indispensible role of the intestinal microbiota in methylating metals and metalloids to volatile derivatives under in vivo conditions, we compared the methylation capability of conventionally raised (CONV) and germ-free (GF) B6-mice fed with chow containing colloidal bismuth subcitrate (CBS) as the starting material for the formation of volatile methylated metal(loid)s. Permethylated volatile trimethylbismuth ((CH3)3Bi) was only detected in the blood of the conventionally raised mice. Concomitantly, a higher bismuth concentration was found in organs such as liver, lung, testicles, and brain of the CONV mice as compared to those of GF mice (P > 0.01), strongly suggesting a correlation between the intestinal biomethylation of bismuth and its accumulation in mammalian tissues